Earlier quoted context omitted.
From a UX standpoint there's a big advantage to monoculture: the user learns a thing once and applies the idiom everywhere. For most users, diversity of options means having to learn every option. They'd rather have one good thing -- or even one good-enough thing. The world does have a variety of options, so users need to live with the fact that they're going to have to discover things, and designers are going to hav…
The problem is that the UI testing monoculture is on Safari. Safari has 20% market share according to StatCounter (9% desktop market share). Most users use Chrome on desktop and mobile.
Anecdotally, most engineers I know use Chrome on a MacBook. The only people I know who use Safari are my parents.