One of the big problems with gender reveals is that they aren't actually that. Gender is based on social and cultural differences between the sexes. What we can tell about a child at birth is their sex (what genitals they're born with). Gender refers to what societal norms are placed on them based on their sex. But we can't call it a sex reveal party, because that sounds like way too much fun. And probably not something you would invite your aunt and uncle to.
Disregarding all of the other issues with gender reveals, doesn't it seem just a bit coincidental that in the last decade, as definitions of gender have become more fluid, this trend to celebrate what your parents determine to be your gender at birth has become so popular? I'm sure those two things are in no way linked, right? In fact, the woman who takes credit for inventing the concept in 2008 now says she regrets it, and the daughter she originally had the party to celebrate is now gender-nonconforming.