I've seen this done a few times and in most of those cases I agreed it made sense. I've thought about this myself a few times too.
But it does lead to unexpected behavior. Users are trained to copy/paste links and send them. If the body only included stuff like auth tokens then it would be ok, but if relevant query stuff was in there (like page size, for example) that would lead to different results that would ultimately be deleterious IMHO.
The copy/paste URL use case is a fair consideration. The places where I’ve seen request bodies on GET requests are APIs [2] that are not seen by the end user.
But it does lead to unexpected behavior. Users are trained to copy/paste links and send them. If the body only included stuff like auth tokens then it would be ok, but if relevant query stuff was in there (like page size, for example) that would lead to different results that would ultimately be deleterious IMHO.