It is worth noting that re-releases are coordinated by the copyright owner. Trademarks are not relevant here. It's also worth noting that most of the games you see that people actually want to play still have their copyrights held by relevant parties. Square-Enix re-releases the Final Fantasy series--and they still own it. Street Fighter or Mega Man re-releases? Capcom still owns it. Super Mario Brothers? Nintendo owns it. Phantasy Star? Sega still owns it.

Most of the games where copyright has bounced around are quite abandoned and not resold at all; in the "abandonware" situation I'd be much more receptive to the idea of emulation to play them. But those are generally not the games that most people pick up emulators to play.