A lot of old games have become unplayable on modern hardware and operating systems. I wrote an article about how making games open source will keep them playable far into the future.
I also discuss how making games open source could be beneficial to developers and companies.
Feedback and constructive criticism are most welcome, and in keeping with the open source spirit, I will give you credit if I make any edits based on your feedback.
Be the change you want to see. Make some games worth playing and release it as a FOSS and prove it can be a commercial success as well. See how it goes.
Asking people to release their work for free while providing very little incentives other than your own benefit aren’t going to convince people who need to put food on the table NOW, without relying on miniscule probability of popularity or success after pouring years of your time.
Well, one of the alternatives is what ID Software used to do, where they would sell the game for a period of time and then open source the code Once sales dropped off.
I have mentioned examples of games that saw commercial success while being open source. And of course, delayed open source is also an option as some other users have said here.