WoW had massive popularity and success that made it a prime target for imitation and chasing the dragon of being the Next Big Thing. I also imagine the sort of "theme park" style of questing and being shepherded from zone to zone is a lot easier to scale up and make large amounts of content, rather than the more sandbox-y and bespoke nature of Runescape content, where you can just run around doing whatever and making your own goals. While Runescape's had a revival over time with OSRS and all, it never really was as giant as WoW, so there probably weren't that many companies trying to follow its examples (not to mention that, as far as I know, Jagex's financials haven't really been stellar, even back in its heyday.) Most RS players would probably stick with what they know rather than try out a new MMO, which also makes it harder to break into the scene (but I wasn't still around in the old EoC days when people started getting iffy on the direction of the game, so there might have been some attempts back then.)
I agree with you on the quests part. You can't really get something like Recipe for Disaster or Song of the Elves in a WoW-style MMO without involving grinding for X drops or just doing a dungeon. I think FF14 does a bit more with its quests and professions and all than WoW, but I haven't touched it in ages, so somebody more familiar with its nuances could probably give a better write-up.