I mean, they do to a certain extent.
Has everyone already forgotten the plethora of tailing missions in EW? Or how about the fish selling mini game? Or unique solo duties like In from the Cold and the siege of Garlemald? There's also a quest where you turn into a frog - this is on top of the already-existing variety mini games too like the carriage stuff and darts shooting.
Now is this the most terribly engaging content in the world? Probably not, but the devs still try to add some degree of variety to the MSQ with each expansion.