“Unless some sort of rabbinic directive is given it will be too embarrassing for people to stop getting gowns. It’s become too much of a given at every chasunah.”
Rabbanim are not going to put takkanos on gowns for weddings. Way too many people have their livelihood in making/selling/renting these gowns that the rabbanim aren’t going to start restricting their use.
I think women and girls like wearing gowns because they like wearing gowns. I don’t think it’s because they’re embarrassed to go without but rather because they are excited that they get to wear one. With all the restrictions on clothing, gowns are an opportunity for a woman to feel beautiful. If the parents can’t afford it, perhaps they can give the child a budget and tell the child to pay for the rest.