Not counting the whole "cease and desist" letters they get.

There are several reasons:
the big one is probably that unpaid workers are unreliable, If they have any skills to speak of they could get a real job at any time forcing you to find replacements and as they have to make a living in some other way while working on the project they can't dedicate alot of time to it.

This problem is made worse by the project manager and everyone involved usually being inexperienced aswell resulting in poor documentation making it really difficult for the replacements you bring in to actually start working and as the project grows in size this can cause a project to collapse under its own weight.

Because they complete 90% of the project. They never complete the next 90%.

All fan-made projects I've closely followed failed. They didn't even get the letters you mention. Main problem? Unrealistic goals IMHO. When they start promising "the best experience based on game X you ever experienced"... I know they'll need to stretch it and they won't be able to.
I'm currently following the remake of an old, obscure NES game. I disagree on their design choices and they seem to be collecting one fail after another but at least they keep it very real about what they are doing... I think they might actually succeed sooner or later!

Is there any evidence that they are more likely to fail than non-commercial projects in general? There will be countless examples of projects that people start, but do not end up with a finished project - indeed, I'm sure even experienced developers who have released non-commercial games, may have their own "failures" in their history. Not everything I write ends up being something I finish, this isn't necessarily a problem.

(Not to mention that plenty of commercial products "fail", if you count everything that a company might start on.)

And if you want examples of outlandish unrealistic goals, just check out the Help Wanted - plenty of "we're going to make an MMORPG" from complete beginners, which aren't "fan" or clones. Actually I would argue that clones have a better chance of success, as you've got existing products that you know are fun to play, to compare against. Where as competely original games have the risk of everyone disagreeing over how to do something, or they finally complete the game only to find it's no fun to play. It's no surprise that vast numbers of even commercial games tend to stick with tried and trusted rehashed ideas.

Katawa Shoujo did not fail. But the guys admit it was much much more difficult than they first expected, and it did take them 4 years or so.

Basically, it's really really hard, and most people don't realize that upfront.

They fail because people underestimate the time and effort to complete them. Most of them are not experienced developers ( of games nor software in general ) and greatly underestimate the development time in that regards ( ignoring that cost of production external to software which is also quite significant ). If your making a game for the first time and have no programming experience, your chances are very slim. As they work on the project and realize how much effort is needed most people then abandon it because they don't consider the payoff worth it. ( 2-3 years of work might be needed ). Unless your going to go into the games industry, for most that isn't a worthwhile investment of their time..

-ddn

Depends on your definition of "fail" also. If the team keeps having to replace people because they improve so much they get full time work in teh games industry, I sure wouldn't call that a failure.

Most likely, I'd guess that when a team realizes that they are working so hard on something they can never publish, it kills motivation. ...if they are not working hard, .. doesn't really matter who's IP it is.

I only knew one guy who's actually received a "cease action" letter. Sucked too, as he had sunk quite a bit of cash into his project. ...don't mess with Lucas.

I only knew one guy who's actually received a "cease action" letter. Sucked too, as he had sunk quite a bit of cash into his project. ...don't mess with Lucas.

Also, don't sink actual money into a fan project based on a pre-existing IP! That's just asking for trouble!

[quote name='GninjaGnome' timestamp='1335214432' post='4934231']
I only knew one guy who's actually received a "cease action" letter. Sucked too, as he had sunk quite a bit of cash into his project. ...don't mess with Lucas.

Also, don't sink actual money into a fan project based on a pre-existing IP! That's just asking for trouble!
[/quote]

Don't sink time into IP you don't have the rights to! Really not that hard to come up with your own characters and story lines. Just put a bit of effort into it some night and create something new.