Funding is also a big part of it. It's much easier to get funding for a mobile game than for an indie PC game, even though the mobile game is significantly less likely to make a return on investment. So perhaps some mobile devs know they aren't going to make it, but take the money anyway so that they can work on something on someone else's dime, while they build up experience and add another piece to their portfolio.

I'm not convinced it's a worthwhile trade, however, if it makes you lose your faith in humanity and your art form in the process.