Rather its first person shooters or zombie games, All types of games are populated with empty or abandoned environments. Is it because it's easier to do? Could be it laziness or lack of creativity?

What is your opinion on the matter?

I'm guessing, but I see a few potential reasons for this:

1) As you suggest, it's easier: one doesn't have to write for, simulate or render lots of NPCs. Note that the inclusion of such NPCs doesn't only introduce inherent complications, but can have indirect effects: for example, adding such NPCs to a shooter prompts questions of what should happen if the player accidentally (or intentionally) shoots an NPC, what should happen when an AI aggressor does it; on top of the design and coding complexity that this produces, it can have a significant effect on the tone of a work, I believe.

2) Abandoned places can be quite evocative, whether its conveying the ravages of war, underscoring the isolation of a hunted protagonist, or simply being eerie, abandoned places can be rather effective, if used well.

3) In the fantasy works specifically, I suspect that a fair bit is owed to the works that inspired the creators in question: works that centre around adventuring in places long-untrod, exploring dangerous lost ruins, etc.

Speculation:

Computers are great at rendering flat surfaces. Man-man structures are flat, so they require less polygons. It's less work for videocards to render a really good looking city than for videocards to render a poor looking jungle.

Want a "natural" area that can look good? Make an abandoned man-made (or alien-made) structure or town. Sure, you can toss some ivy and vines, trash, bumpy ground, and such, but predominately, it's a bunch of mostly flat surfaces on top of mostly flat terrain. (By 'flat' I don't mean level - it could be a flat surface sloping downhill)

Other good choices: Caves, canyons, deserts, mountains, other locations without a huge amount of plants.

NPCs are expensive to do well, but other than that people-free areas can give the player the feeling of being free to do things that other people block them from doing in real life. It's like a frontier.

Could be it laziness or lack of creativity?

Yes, game developers are known to be lazy and lack creativity. They're just not as cool as the folks at OfficeDev.net where users ask questions like "why doesn't Word render all my movie scripts into Peter Jackson epics? are you guys just lazy and lacking in creativity?"

If you mean the question in terms of "why are so many areas sparsely populated" its really very simple -- the kinds of machines that mainstream users have are really only capable of doing so much per frame, whether its drawing, processing AI or physics, or streaming data from the disk; you have ~16ms to do everything that needs to get done at 60hz. At the current time, a "mainstream" machine is either of the two most recent consoles Xbox One or PS4 -- so 8 threads, each with 3ish instructions in-flight, running at around 1.6Ghz, 8GB RAM, a Radeon GPU with between 768 and 1152 shaders, and a mechanical hard disk. Given the limited resources, you want to spend it on things that matter -- not stuff that's essentially eye-candy.

But even sparse content costs money to make happen, so its unfair to say its presence is lazy -- its only there because they spent time and money on it, so you can be certain that it has a purpose -- perhaps the twisty, drab corridors you have to march through from one location to the next allows the old textures to be freed from memory while the ones for the next area are loaded in (you can think of the corridor as an interactive loading screen), or perhaps the developer wanted to create a feeling of space in a cost-effective way, or wanted to communicate that here was once a bustling community now a ghost town, or perhaps, even, that there was an important scene here once that was cut from the game, and it would take too much time and money too late in the schedule to remix the area with something less bland. Reasons abound, but there always is one.

There are games that don't just render abandoned places. Just look at the Dead Rising Series or GTA or even Farcry 4, for places chock full of NPCs. So no I don't think its because of technical limitations.

I think its because abandoned places are so much "cooler". Just look at all the photography websites that are dedicated to taking pictures of abandoned places and the popularity of Documentaries like "Life after people".

The type of environments used are places that you can't just go and explore without getting arrested.

Also if there was an epic gunfight somewhere I think the majority of people would flee anyway meaning that even if the place wasn't abandoned it soon would once the action kicked off.

In addition to the reasons above, it's also that ruination allows you to guide the player along interesting paths without having an entirely lunatic building/city. So if you look at real buildings and cities, they tend to allow a lot of paths (for convenience, safety, etc.) but also none of those paths are particularly interesting. You often get to places by straight lines, don't change floors by climbing out windows, don't often change elevations, don't get inside by climbing through vents, etc. There's not much spatial variety in normal human spaces -- we have a grid of streets, and buildings have floors, and floors have hallways, and hallways have rooms coming off of them. Huge amounts of freedom, very little variety.

But on the other hand, creating interesting paths by building it into the layout of the city/building results in some odd buildings, odd enough that it can break immersion. I remember classic games where there's basically a single intended path through the building, maybe where you're climbing up precarious things, going through airvents, etc., and reviews would say things like "Clearly people work here, but how in the world do they get in and out of their offices?" "Why would the architect make people go through a winding hallway in order to get between adjacent rooms?"

A ruined city gives you interesting paths without necessarily sacrificing the illusion that it's a real place. You can keep the player constrained (barricading streets where there's nothing beyond them, collapsing hallways and stairs, having all elevators be broken) without suggesting that the actual inhabitants of the city are/were likewise constrained. And it lets you make those constraints big and dramatic -- collapsed buildings and the like -- rather than suggest that your supersoldier or whatever might be stopped by a pile of barrels, an old-fashioned wooden fence, or some guy standing in a doorway refusing to move.

Realistically, if there were reports of some pimply newb with a claim to have consorted with my 80 year old mother running around my neighbourhood with fully automatic weapons and a virtually unlimited supply of ammo fragging anything that moved, I, my family, and all my neighbours would be likely to abandon the area too.

Apocalyptic environments also mean you can do anything you want.

I also don't like how modern 3D RTSs are virtually devoid of trees. The tree count significantly goes down in 3D.