I guess HTML/CSS is something that can be done by a non programming designer, so if your team is large enough to have separate back-end devs , front-end devs and designers it's more important for the developer to be able to manipulate CSS than design it from scratch.

Bootstrap and the like made HTML/CSS a second class citizen for business apps for a while now.

yeah most front end devs I'm familiar with are layout first, and just have to hammer on the JS until it works. I like the front end engineer title for JS first.