massive multiplayer (depends how you define massive) is kinda the next step.
give games color, 16bit 32bit and on and on, 2 player, 4 player, 8 player, 1v1 ip games, network games, then the internet now supports 32/64/100s/1000s of people at once.
they follow the money. and to compete with developers.
if single player games are becoming less popular, at least with PC, then developers will follow that money