Comment by ehnto

As others have mentioned, it's being used when writing components. Why does it work so well for components though, since you could just as well still separate the CSS? I think it's because of code co-location. Everything that describes how a component looks and functions lives in one file only. That's also why inline styles and utility libraries are palatable now, it's easier to reason about if it's described directly on the element, and you don't need to remember to update all usages of the inline style since it's a re-used component. It's even one step less indirection than using class names in that context, which is handy.

I also think most people are quite bad at organizing CSS, so I'm personally thankful for this change even though I love a well organized simple CSS/HTML site. It means less projects I inherit are rabbit warrens of legacy CSS to unravel.