It's a smaller market and it's more difficult to develop for the PC. Unfortunately, calling it quits to PC development isn't going to help the problem. Raise your standards of quality and focus less on raw technical prowess and more on getting your games working well and properly for your users. Advertise them and market them to more than just the hardcore PC gaming demographic. There's a lot of PCs out there and PC gaming is huge (in terms of online/Flash/older games), but since most computers can't run the latest titles, everyone tends to ignore it. Hardcore PC gaming isn't going anywhere either, but exclusive games might become mostly indie fare within the next few years.
It's funny how a lot of people chalk this up entirely to poor PC game sales, but a lot of it actually has to do with the high cost of developing games these days, period. Players expect excellent graphics and audio, and that takes the most development time and effort by far, not to mention the most manpower. Publishers want to make as much money back as they possibly can, and along with limiting used sales and using downloadable content to bring in more money for comparatively much less effort are a couple of other ways they do this, too, but multi-platform development is practically a necessity these days to bring in a profit. When your game costs $20-50 million dollars to develop and promote, you'd damn well better believe it needs to sell well.