Ryan does a fairly well job on describing what people are missing on the technical level. But that's only part of the story; I'll develop on the other, dark and boring, part spectrum which is often ignored: You see, game development is really a controlled business. Let me elaborate (by still simplifying a lot of stuff).
You have time, human resource, etc., all of which are finite resources and ultimately a cost that you allocate on a budget. To balance that, you have to make sure that it will bring in not only the amount you paid to create the game, but more to turn in a sizeable profit. Why work on something that will bring you $10? (Or a magnitude more, if you're talking as a company). It's not a charity.
As everything you do costs money, you'll have to justify how working X would hold more value than Y, as an individual, and even as management. Should the answer be that what you're working on not what is planned/acceptable/not valuable enough, you'll be directed to work on something else, or be shown the door as it is their money that you, as a developer, are spending after all. There is very little time for experimentation. And even if there were, you'd be allocated a fixed amount of time doing that compared to something that brings sure value.
As much as possible, the roadmap of things to do is planned. But sometimes, things don't go as planned (Hah! Okay I jest: Always). You can't always extend the time of the project, because that would increase the planned budget. Instead you'd just have to cut on things that has the least value, or that cannot be done in time for sure. The planned revenue stays the same no matter how much additional work you do.
And lastly, say you get in the team as a developer, for example as one that has the skillset to develop a game engine; You likely won't get to fully participate (or even at all) on other aspects such as level design, setting, story. In more complicated project (as soon as you hit 3D, you likely get in this category), you may not even have anything to do with what you think you can tackle, like anything graphic (lights, particle and effects, animation). There are other, better people suited than you for that after all. Ultimately, you're a simple small gear as part of a whole game creating machine. When participating in these kind of projects, your individual contribution, while important, means little in the grand scheme of things.
Also, It's really not an all-fun industry, and many people fail to realize that.
Project Mania seems to have have put some ideas in some people's head. I'm not undermining the work our 2-D devs are doing, but the fact is that typically, 3-D projects operate at very different scales.