There are plenty of projects where frontend/backend is a logical way to separate things, in which case it can be much more cost-effective to hire frontend specialists. Not only are they more familiar with all the specialized tools, but they can also do it with only bootcamp education.

I've been in teams with generalists only, and yeah we can all deal with UI, but it takes longer. No matter how good someone is, they can't have every detail fresh in their head all the time.

Or what about a full stack that's backend-backend, in a large corp with multiple internal services talking to each other? Only the higher-tier engineers have a good understanding of all the teams' moving pieces, even then not so deep.