I would imagine it has a lot to do with the programming language and other technologies in the project. The LLMs have tons of training data on JS and React. They probably have relatively little on Erlang.
Even if you're using JS/React, the level of sophistication of the UI seems to matter a lot.
"Put this data on a web page" is easy. Complex application-like interactions seem to be more challenging. It's faster/easier to do the work by hand than it is to wait for the LLM, then correct it.
But if you aren't already an expert, you probably aren't looking for complex interaction models. "Put this data on a web page" is often just fine.
It's like when your frat house has a filing cabinet full of past years' essays.
Protestant Reformation? Done, 7 years ago, different professor. Your brothers are pleased to liberate you for Saturday's house party.
Barter Economy in Soviet Breakaway Republics? Sorry, bro. But we have a Red Square McDonald's feasibility study; you can change the names?
Mass of learning material doesn't equal quality though. The amount of poor react code out there is not to underestimate. I feel like llm generated gleam code was way cleaner (after some agentic loops due to syntactic misunderstanding) than ts/react where it's so biased to produce overly verbose slob.