Yeah, I've found LLMs to be pretty decent at frontend stuff.
I got a new job recently and my main task has been overhauling a Claude generated app into something functional. The backend is an unsalvageable disaster, but the frontend is actually pretty good. Which is great for me because I suck at UIs.
I think if you have a solid backend already in place, an LLM can produce a pretty functional frontend with far less effort to fix up.
I think that has more to do with the fact that JS is the most popular language in the world, especially available code to train LLMs on.
Backend code is far less likely to be available because it's more likely to be closed source and is spread over many languages (Java, Python, C#, JS, Ruby, Go, PHP...).