Well I'm saying work on what you want to work on and it's absolutely fine to abandon games when you think you've detected the direction is not good. Finishing a game is very, very hard. You will almost inevitably encounter problems that require skillsets you don't have and aren't interested in learning. If you could to a place where a game could be finished, then hire a team to help you finish it. Otherwise you'll spend too much time learning skills you don't like or need (personally) to execute on a vision. For most indie devs, in my estimation, that's mostly a question of hiring artists to make it look nice and designers to grind out content for the game (e.g. levels). I think you can presume that most people that want to be "indie game devs" want to be creative directors with just enough skills of their own to prototype something successfully. And I encourage that.

The co-op thing is just a perceived niche of under-served market demand : effort required imo.