That and they do not necessarily generate better code. They tend to generate code that is repetitive. It misses opportunities for extraction and refactoring, the result is bloated and hard to read code (because those blocks are there literally instead of with a usable name) and they tend to over-comment where it doesn't add but is 'safe' because it is obvious (effectively re-writing code as comments) and fail to document where documentation would be essential. There also typically isn't any real plan to what is written, as long as 'the tests pass' it is all good.

You can fix a lot of this stuff by shepherding the whole process but it can get quite tedious. I'm impressed by the number of people that are letting Jesus (one of these days an AI provider is going to name their AI that way :) ) take the wheel and I wonder how long they will manage to support the output. So far the score isn't very good. I've gotten good mileage out of these tools by letting them loose on very narrowly scoped pieces of code that are written in isolation. As soon as the codebase gets larger than 100K LOC or so managing the whole thing becomes an exercise in putting up barriers to avoid spillover from a tiny issue into a much larger one.