I don’t understand the big deal. As puzzleannie said, the comparison is not analagous. There is not an analogy between HFC veils and wedding veils, either.
My parish growing up, the parish where my eldest made her FHC, and the parish where my next daughter made her FHC all had the first communicants come to May Crowning in their outfits.
I also wore mine fo 40 Hours Devotion Procession, as did the other nine girls who had dresses. It was right after Vatican II, and parents were encouraged to let their girls wear slips under these hideous white robes. We wore them with our veils.
The eldest wore hers with her fancy ponytail holder, as she refused to wear a veil. The next daughter wore hers with her veil.
I also wore mine for a party dress, as did my friends who had them. They were shorter than FHC dresses nowadays, and little girls dressed up for parties. I took care of it, but when I outgrew it, it went to Sister #3, who wore it for her FHC, et al. These dresses, even back then, cost too much money to sit in a closet and not get use.
You are about the age of my eldest, OP.

I don’t understand why it effects you so.
It just occured to me that seniors, particularly the down-right elderly whose children don’t bring the little ones to visit, LOVE to see babies in their baptismal gowns, and the first communicants in their finery. Maybe your pastor was just trying to give the older generations a little joy in their Sunday.