Echo JS 0.11.0

I'd say that it largely comes down to the fact that newer CSS features are increasingly complicated, compared to what people are used to.  Many have already learned less, scss and/or stylus and rolling back those things to go to more canonical css is harder.

Beyond this, many UI toolkits have already abstracted away many of the aspects on your behalf to give you a good usability level.  I absolutely love what's in the box with material-ui, and every time I have to tweak flexbox layouts by hand, if feels like pulling teeth, figuratively speaking, it just isn't pleasant in any way, shape or form.

It's all very cool, transitions, flexbox/grid, variables, imports and more... In the end, there's a certain amount of entropy to overcome, abstraction to get past and things to learn.

This also doesn't even get into the fact, that many developers turn down their noses at technologies the closer to the UI that you get.  JavaScript itself to this day suffers in this way, I see it often from Java and C# developers.