Nintendo makes a lot of money rereleasing games. You might not be able to buy an n64 or a copy of mario 64 new anymore, because they aren't manufactured anymore. But people will pay for a rerelease of mario 64 on the wii or switch, possibly highly (a bundle of 3 rereleased "unavailable"mario games was going for $50-$60 new on switch recently).

Also the games aren't 100% unavailable, they're perfectly available on their original platforms on the secondary market if you want one badly.