I think that's mostly a bad assumption (people who think most players don't want interesting job design, I mean) that stems from a very bizarre notion that job complexity means do the rotation correctly and optimally or fail the content. Which in all fairness was never the case not even in the notorious Heavensward. But for some reason, a lot of people have come to treat optimal rotations as the entry point and raising the ceiling means anyone who can't do it perfectly is going to suffer constantly hitting 1% enrages. But really, I would argue that sentiment comes from a subset of players even smaller than the group of players unhappy with oversimplification--people who want to be perfect at their job but have no desire to put in any effort to learn it. There was a Misshapen Chair video that talked about that mentality in gaming, and his term was a not-so-friendly one.
But I don't know if I believe that's entirely who the design team designs jobs for either. I think it more prominently comes down to something that's been said here before is it's easy for the designers to balance. Rather than take the time to properly design and balance jobs that are still fun and engaging to play, they'd prefer to cut corners and aggressively simplify jobs so they don't have to work hard at job design. They've probably been cutting corners on job design for so long because of constraints on the budget and the schedule paired with the ever increasing number of jobs. Spend more time over designing fights that apply to players universally and minimize time spent actually thinking about and adjusting job balance. I am sympathetic to the issue of restricted resources, but job design should not be an area we are slacking off on, especially when the balance ends up janky anyway.