Some of that is seeking to kill competitors before they can get established. That's normal and has been around for generations, if not since trading was invented.
But most of what we've seen during the "enshitification age" has been to burn money until you achieve a critical mass of users. However, this only really applies to social platforms where the point of it is communicating with people you know. That's the lock-in. You convinced Grandma to join Bookface and now you feel bad leaving if she doesn't leave at the same time, and more importantly, who wants to join Google Square if nobody else uses it?
That's not going to work for AI platforms.
What I do see potentially working is one method that email platforms use to lock in users: having tons of data you can't export/migrate. If you spent lots of time training your AI by feeding it your data, that's going to make it harder to leave.
So far none of them have capitalized on this (probably due to various technical reasons) but I expect it to start eventually.