I think the numbers are actually quite a bit lower and if you look closer a lot of young women identify as bisexual not gay or trans which is not surprising given the current asexual state of the young male. Also, I suspect the proliferation of free porn has something to do with it where it’s a most common fantasy of men to be with more than one woman who the fantasy requires to be bisexual. See these interesting stats at Gallup https://news.gallup.com/poll/329708/lgbt-identification-rises-latest-estimate.aspx

I think the actual number of born gay and trans people remains steadily nominal while the choice "bi" is more of a trendy stance to take against the patriarchal setup. I would bet that the number of these who grow up later to be in bi or gay relationships diminishes accordingly to historical levels or slightly higher for lesbians.