For me, it’s the decision fatigue. The content is so fragmented across so many services and it’s constantly getting worse. The rising costs adds to the fatigue because the fragmentation is less manageable now with all the services raising prices and cracking down on password sharing. I just feel like I have to think about it too much now.
Have you tried Itch.io? They have a lot of Gameboy and NES roms that are “Name your own price.” I don’t have any recommendations - I’ve just started poking around with homebrew roms myself.