Argument reduced to nothing: why not do some hack-work to make money in order to fund your own interests?
A reasonable argument indeed. However, if you've just done quite nicely making a Match 3 in three months, are you really going to want to invest some or all of the profits into making a game that might not ever be finished, might not turn out very good or might just not sell because the market doesn't want it? Or are you always going to be tempted to write "just one more" Match 3?
Speaking from personal experience, it needs a great deal of willpower to stop writing for a market ( any market ) when you know it's working and fairly safe and you could do it again, and turn to your "pet" project which could earn you nothing at all. I guess less so if it's only in your spare time, but still..