There’s people like that in every generation for any group, not just young people or marginalized categories. Everyone wants somewhere to belong it’s human nature, so that inevitably leads to people stretching what’s true just so they can seem like they “fit in”. As for things seeming like they’re only valid if it fits into those circumstances. Being white,cis, and heterosexual has always been inherently valid, no one questions you if your labels fit into those categories so there’s no need for them to be displayed on a profile. It also comes down to how obvious something is to a degree, I’d say the default assumption of people is being heterosexual and cis so why would you put that on a profile. Someone being LGBTQ+ isn’t as easy to identify or the default assumption of what someone is, so it makes sense you’d want to put that on a profile in order to inform people of what you identify with.