WB is MGM's new home entertainment distributor since Disney bought Fox, if MGM wanted to release a UHD themselves it would be through WB and Universal's joint distributor, Studio Distribution Services.
It’s irrelevant to whether things get released though. They put out what MGM tells them to, as I understand it.
I'm guessing they might only release the theatrical version in 4K that way, if at all, since that's what they did on BD (and even reissued that BD 2x in just a few years after the original, decade-old release). Of course, that (all) was also long before Amazon acquired MGM.
What's probably more likely at this point is Amazon just (eventually) makes it available for streaming in 4K, especially if the previous old scan for that old BD was already done in 4K. I definitely wouldn't count on them putting it out on 4K disc thru Warner/Universal for the foreseeable future...
_Man_