You know, this speaks volumes. Layout is a complicated business, sure, but CSS just keeps having monumental shifts in how you're supposed to approach it year after year; it's as if it's done without any overarching theory/vision but merely groping in the dark, trying things and fixes, and seeing what sticks and doesn't suck too horribly (this latter part is optional; remember Yandex's BEM?)
Would you prefer that CSS never evolve, and our frustrations remain the same? Writing CSS today has gotten significantly easier with flexbox, variables and now nesting. BEM is not part of the CSS spec, that's just a design methodology.
You really don’t have to change your css. My personal website has been using roughly the same css for a decade. Why not?
Sure if you are a designer and want to follow trends, you’ll have to keep your css skills up to date. But for most websites, you can use css from a decade ago.