There were a bunch of (online) games without a well-defined end popular in the late 90s/early 00s too.

https://en.wikipedia.org/wiki/Diablo_II

https://en.wikipedia.org/wiki/StarCraft:_Brood_War

https://en.wikipedia.org/wiki/Asheron%27s_Call

https://en.wikipedia.org/wiki/EverQuest