Of course there are exceptions. But for every piece of software that's still making money 15 years later, there's 99 pieces that are totally abandoned. Often it's difficult to even figure out who owns the rights and how to contact them.

Even the works that are still generating revenue after 15 years, surely most of them have already made 99% of the money they are ever going to make. The people buying rebel assault now are just a few nostalgia seekers. It will add up to a tiny tiny fraction of the total copies sold in it's heyday.