Personally I still find it really helpful to have a proven framework to rely on so that I can be confident I'll have a reasonably consistent looking UI across a range of browsers, browser versions, screen sizes, and OS even versions.
Bootstrap was/is popular for the same reason. One framework and your site looks decent on almost any device. The downside is a bit like LLM work in that it all ends up looking like a Bootstrap site unless you’re a good designer.
