Flash games and to a lesser extent Java applet games used to be very hot. Back in 2005 or so i paid rent with a game i made in literally an afternoon in Java.
However the largely "casual" market who played these games switched to mobile phones and any remaining "hardcore" players switched to Steam, which in meantime opened up to developers.
And from a technical side, it took years for web tech to reach what you could do with Flash when the latter was forcibly killed.
The market for other types of players is there and it's far from niche. It's more like making games for them isn't as lucrative. Still pays well for sure, but you can make the same or better working in a corporate office like everyone else. Ironically, office drones are probably the ones who most want to make and play these games.
