There's an unfathomable number of games that were released on the Commodore 64, Amiga, Atari ST, and most famously DOS that were made by one or two people, self-published, and have now completely fallen into obscurity to a point where it's not 100% clear who owns the copyright and who to give money even if you wanted to, which has led to the "probably-illegal-but-not-really-enforced" term of "Abandonware".
I honestly kind of think that Abandonware should be codified into law in the same way that trademarks are; if you're not actively giving me a legitimate way to buy your game then I don't think it should be illegal for me to get it illegitimately.