My most successful game was an app for iOS which made me a grand total of around $30. The difference is I only spent around 80 hours working on it (40 or so for the game, 20 or so on the level editor, and 20 or so making levels). I had no money for marketing, had done no research beforehand, so I pretty much knew it was going to fail but did it as a fun side project to learn some new stuff and for my CV.
Compare that to the various website side projects I've worked on over the years which have made me hundreds of thousands of dollars (over 10 years). Game dev sounds fun, but if you're looking to make money, I would definitely stay away from it.