Games however have not.
There are two flaws in this argument.
The first is that they actually have, even when you adjust for inflation. The Sega Megadrive's RRP at launch was £189.99 in the UK and games from £19.99. Adjusted for inflation you're looking at £300 for the console and £32 for a game. The Playstation 4 on the other hand retails for £350 and the Xbox One at £430 - games on both systems are priced from £45, but often reach £60. Whilst the cost of the consoles might not have climbed massively - 16% and 43% respectively in this example it is still an increase. Games themselves have increased between 40% and 88% in price after adjustment for inflation.
Let's not forget that games in 1990 didn't include £40 DLC season pass / premium edition on launch day and / or (in the case of Forza as an example) a potential £3000 worth of IAPs. Those four Call of Duty DLC map packs per year (the type of release that used to be for free in the past on the platforms that supported it) are a whopping £60 on your initial £60 investment - if you go so far as to include that kind of additional expenditure, games have increased in price 375%, though this is more arguable and brings the debate as to what constitutes the original game purchase.
It's a common misconception that seems to be heavily perpetuated at the moment that games are not any more expensive to buy than they were before (I'm wondering where the origin of this widely perpetuated 'fact' has come from).
In any case, these IAPs for 'buckets of gems required to progress you a level' are more expensive than an entire game was 20 years ago, even adjusting for inflation.
The second issue is something called economies of scale. The more of a product that is produced, the cheaper it can be sold - it's an (almost) infallible rule of modern manufacturing. The newest consoles have sold millions of hardware units in their first week alone - some games have sold in excess of two million copies on week one (along with season passes!) - a third of what the biggest games may have sold on former consoles in their lifetime (Sonic the Hedgehog was bundled with the console and managed 6 million copies!).
So whilst development costs may have risen, the player base has risen too. When you have 27 million active players like some games are now boasting, you have more players than older hardware units were even manufactured.