There are certain plays that the addition of music either as a musical play, musical comedy or opera, adds nothing. Streetcar as an opera had no imperative to be musicalized. The words already 'sing'. There is no reason for any musical version to be done.
This is the fundamental problem with any musical version of Cyrano, for instance.
Auntie Mame (which star Roz Russell called 'a revue without music') is a better piece than Mame ever could be for the same reason, and Mame isn't a bad show. Auntie Mame is just better.
A basic question that the writers of any musical need to ask is "Will the addition of a musical score tell this story better?"
Look at Dracula. Better yet, don't.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher