During one of Mike Mearls' sub-class building streams he was asked why he doesn't just include some options as feats. His response was that less than half of all tables use feats.
I bet multiclassing is even less than that.
We have what, over 20 million 5e players now?
I agree with the others saying to take these stats with a high degree of skepticism.
It's easy to not be exposed to all the people who play differently.
Seems like people forget that feats are an optional rule and not assumed to be in every table by default. However, I wonder if the number of tables using D&D Beyond use more feats and multiclassing than those that don't. Of course, that's just speculation without data but it would not surprise me.