This is true, but in gaming, open-source projects often have huge, incredible impact, which often goes way beyond their original scope. For example Doom sourceport GZDoom is nowadays often used to create completely new indie pixelart or retro-style shooter games, Morrowind sourceport OpenMW is also to my knowledge have started being used in standalone projects. It will take just a single open-source project that covers MMORPG genre somewhat decently to become a solid foundation.