Here's my two cents: They are all very openly gay-supportive. Judy was Hollywood's ugly duckling, everyone knew she was great, she just wasn't beautiful and so MGM didn't really know what to do with her, sort of what happens to many gay guys. While they may excell in whatever their job is, and be great friends, many employers, friends and family members don't quite know how to go about the whole "but he's gay" issue.
Also, Judy never really belonged anywhere, just like the gay men of the 40s and 50s, and so she sang to them and about them in a way. All on the same boat of not belonging, but always longing and hoping.
I don't want to go on about the rest, but this is the general idea.
The meat is always leaner on somebody else's dinner plate!