There are plenty of commits that don't need an explanation like mechanical cleanups or refactoring. If your code is appropriately documented then an LLM can often extract the explanation too.
A fix often has a particular bug it’s addressed, the bug should be explained in the commit. A refactor has a reason, that needs to be explained as well.
I’m not saying LLMs can’t do this, but it needs the context and it’s rarely in the diff of the commit you will find that.