It is really hard to do it all on your own without a studio. The analogy is trying to out compete Coca-Cola with your own brand of similar soda. Just because your formula is good doesn't mean you get success. There are other factors. First you need to get the overhead to even produce the soda. Then you need to marketing so people know your cola exists.
There's not a whole lot of money in it for amateurs compared to how much work goes into them. There's also a degree of luck involved. I think the people who made Angry Birds had made 40 some other games before getting success. Of course they just stole the idea from Crush the Castle with cutesy graphics. Candy Crush did about the same thing. They stole someone else's games directly, then sued the guy who made the game before them.
The only reason I'd suggest anyone get into video game making is that you love video games so much. I decided to be a video game programmer/designer back in 1987 when I played most of the NES/C64/Atari/Arcade games. I was bored because I played all the games that existed and wanted to make better games. I just felt the future was a MMORPG, multiplayer online and lots of action oriented RPG. Of course they didn't call them MMORPGS back then, they were just online RPGs games with a lot of players. People talked about these things because of what Quantum Link was doing.
I've been making games since 1992, and have very limited success mostly because I tended to get too ambitious when I first started. Here is a game I published just 2 weeks ago. Throne and Crown
No one beat this game yet even though its only about 10 hours long. My next games I'm making with the idea that I'm making them out of a love for a game I'll enjoy over trying to script a game other people might. So I'm going to probably take the good engine from TAC and then make it similar to Angband except action oriented. Also I have some cell phone games I'm toying with making, but they're a long way off.