Because as a fattie with massive boobs I need to see if a bra is actually going to be any good for me.
My friend is an A cup. She can wear literally any bra because there's nothing to support. My H cups need a bit more.
Having said that those bras are so badly fitting it doesn't help.
They aren't pornographic though @Arapawa . Just slightly sexier than your everyday bra. My friend (slim, mid 20s) wears similar ones with the straps showing under her dress. She looks awesome. I'd look ridiculous in them, but I'm 12 years older and much much bigger.