I imagine it might have something to do with the fact some people start their project then come to realize just what involved and over time it just eats away at them.
Oh, absolutely. You start too big, realize it's not easy, or it's not as popular as you imagined, you lose motivation and things spiral down from there. There are also very legitimate reasons to call it quits (if you are trying to make it your full time job but things don't work out, you can't sink infinite money in the project that was supposed to MAKE you money), but most of the time it's just people jumping right into big projects without having even tried their hands on smaller ones.
It's much easier to finish a small game, even when things go wrong (assuming you aren't completely lacking in the required skills, that is). Nowadays, especially with Patreon around, not many go for projects that build experience (well, this was a problem in the past as well, but I really feel like crowdfunding exacerbated the issue).