10-20mg isn't "horrifying" per se, but it's pushing the dose further down the flat line of the dose response curve which leads to a greater likelihood of adverse side effects. Myalgia, tendon issues, insulin resistance all occur at higher doses. A max dose of Atorvastatin generally yields type 2 diabetes in 1/3 of patients after a few years, a fact which then causes me to wonder why in the fuck anyone would want to push statin monotherapy to the max dose.
Rosuvastatin and Atorvastatin are fundamentally different in how they are metabolized. Yes, they are used interchangeably, but that doesn't mean they are the same. Rosuvastatin is more potent on a per milligram basis. Is hydrophilic, doesn't cross the blood/brain barrier, nor tax the liver quite the same as Atorvastatin.
I personally believe it's just inertia. The clinical trials (from a couple decades back) all used very high doses to guarantee a positive response in a population that was at very high risk for whom anything other than the max dose would have been unethical. Which has led me to the conclusion that the medical community is really focused on treating MACE rather than the disease itself. As though it's inevitable that you're going to have a heart attack, but once you do, they'll treat you.