It was a bit of a cultural zeitgeist in the 2010s. A lot happened with popular culture being more pro LGBT, and that translated into more people becoming LGBT.
It makes sense. When more people are comfortable to come out of the closet, more people end up knowing gay people. And that leads to people realizing gay people are no different from everyone else, which leads to pro LGBT beliefs.
What I find fascinating is that we’re seeing what the natural distribution of sexuality is for people. Based on Gen Z it looks like it’s much higher towards bi and gay than we previously thought.