How are they morally obligated (or suggested) to provide access to older games?

I view the morality around IP law as an implicit contract with society. Actual theft is wrong because I am depriving someone of something without their consent. Pirating is wrong because it disincentives the production of further work. If there's no option to pay, then piracy doesn't affect the incentive structure at all, except possibly sending a a signal that there's still demand there.

They're not, but people are morally entitled to pirate them if they don't.