When you dig into the data of several other surveys, it becomes even more apparent that the seemingly rising number of LGBT+ is due to the removal of stigma: Earlier surveys had shown that the group that saw the biggest growth among all are bisexual/pansexual people while the other groups saw much less growth.

From an article in Psychology Today from 2022:

In the Gallup survey, most of those identifying as LGBT+ said they were bisexual: [...] 57 percent of those declaring themselves something other than cisgender heterosexual. [...]
Again, bisexuality was age-related. Those most likely to declare themselves bisexual were the youngest adults, with each older age group less and less likely to claim bisexuality.

An article in the Washington Post from 2021 makes the apparent "rise" of bisexuality/pansexuality even more obvious:

Research from the Williams Institute at the UCLA School of Law has similarly found that a key driver of the growth in the LGBT community has been a surge in bisexual women and girls. Bisexual women make up the largest group of LGBT adults — about 35 percent, according to a Williams Institute analysis of data from three population-based surveys. More than one in 10 U.S. high school youth identifies as lesbian, gay or bisexual. And among them, 75 percent are female and 77 percent identify as bisexual. [...]
Kerith Conron, research director at the Williams Institute, said more research is needed to understand this pattern. But, she said, “my theory would be it’s more acceptable for girls to identify as bisexual. The policing of young people is particularly pronounced for boys, to be masculine,” Conron said. “And for girls, to be bisexual isn’t necessarily perceived as a significant deviation from femininity.”

So people are much more open to talk about their sexual desires for people of the same sex once the stigma is removed, but - unfortunately for young men - that is less often the case for them, so they won't admit these feelings.

PS: Add that to the fact that women are much more likely to hold progressive politics than men.