The majority of the games on most Nintendo systems are third party. Nintendo doesn't own the IPs and doesn't have the legal right to list them for sale. It's also rather unreasonable to expect them to let you own a game forever AND continue to update the emulator. If you've owned something for, say, 10+ years, nobody is under any obligation to keep supporting the service for that product, no different from how my SNES and my games for it are no longer under warranty and I can't expect Nintendo to still offer maintenance service and such for them. I can keep them forever, but I'm on my own with them past a certain point.