And this is the thing that many web developers miss. As they've begun to creep into the mobile and desktop space, intent on replacing native experiences with a continual barrage of non-native, bespoke apps, each with their own design, they've mistaken widespread availability with quality and utility — that HTML/CSS UIs are widely available is all to do with ubiquity and lessening an otherwise not-at-all steep learning curve, not technical merit.
Give me springs and struts, Autolayout, or PowerApp's style declarative positioning any day.
Positioning is one thing, but CSS really shines in it's graphical abilities. Autolayout is fantastic, but have you tried writing the custom CoreGraphics code that is required to do anything outside of standard UIKit visuals? Not fun [0]. Being able to just type `background: linear-gradient(orange, green)` is a godsend compared to that stuff.
[0] https://github.com/amraboelela/myos.examples/blob/master/Cor...
At this point, I'm starting to look into things that "transpile" to CSS.
One being that practically all software nowadays are webapps and there's no choice. For those that aren't webapps and whose GUI toolkit use CSS or something like CSS, it's probably to try to pull people that already have experience with webapps.