Question about underwire on bras

[Horseinahat]

What do the underwires actually do?
Before I had seen an underwired bra I imagined the wire somehow supported the tissue in the cup but it just sits against your chest. What am I missing?
I almost always wear a sports bra with underwiring!

Bumping to see if anyone really knows.......

I’ve found this linkon Bra Theory.

I've not seen that website before. Interesting. I don't think I understood 'the underwire is a fulcrum theory' though. Did you?

Thinking about wired vs non wired on me, the wire pulls the fabric of the bra right in to the curve of the breast in a way that just isn't possible without it. That means the cup can lift and separate the breasts. Wiithout the wire they're always some variant of squashed together monoboob.