HTupolev

I'd argue that almost everyone is a complete idiot when it comes to working on, adjusting, or servicing rim brakes as well.

The difference is that hydro discs aren't tolerant to things being done badly. There's effectively zero springiness in the hydraulics, and the mechanical advantage curve and engagement point is determined by the paired mechanisms, so it's either close to correct or totally wrong. Outside of rotor rub, a freshly-adjusted hydro setup doesn't have much room between "works perfectly" and "doesn't work at all." Like, if you sequence a hydro bleed incorrectly, the process looks almost normal, but you can easily end up with no braking at all, and you won't know what happened unless you understand what's going on inside the mechanism.
With rim brakes, you can use cheap springy unlubricated housing with unlubricated cables, you can route that housing with tons of tight bends, you can set up a centerpull with abysmal geometry and neglect to pre-bend a stiff straddle where it exits a narrow yolk, you can neglect to stick a ferrule in a place where a ferrule is supposed to go... you can do all kinds of things that result in awful braking, while the brakes still "work."

I suspect this is part of why even many dry-weather road cyclists were easily convinced by hydro discs. When comparing a dubious rim setup to a near-perfect hydro setup, the near-perfect hydro setup is going to feel loads better.