LLMs are pretty good at anything that follows a pattern, even a really complex pattern. So unit tests often take a form similar to the n-shot testing we do with LLMs, a series of statements and their answers (or in the case of unit tests, a series of test names and their tests). It makes sense to me that LLMs would excel here and my own experience is that they are great at taking care of the low-hanging fruit when it comes to testing.