What is it about the Supporting Female?

So we know by now that there is a long list of Supporting Female roles in musical theatre that are incredible, but why is it there are some that are considered the best in the whole show or more iconic (as opposed to the leads in some cases!)? I've wondered this for the longest time. Why do we identify with them most? As an gay man, why do many of us idolise not only these roles but the women who play them? and more interestingly, why do ao many iconic females want to play those roles?

To name a few to get an idea of what I mean: Anita (West Side Story), Joanne (Company), Candela (Women on the Verge), Carlotta (Follies), Angelica (Hamilton), Cassie (A Chorus Line), Matron Mama Morton (Chicago) and Rizzo (Grease).