The simplest explanation is that it's 'acceptable' to be trans in 2019. Plastic didn't make people gay, but the gay population increased in the mid to late 1900s just as the trans population is increasing now.

There aren't just the social factors with coming out, but also the education around being being trans. Some people live their entire lives not knowing and only find out after watching youtube, meeting people in the community, or going to therapy (which is also becoming more commonplace and acceptable). The stigma attached to trans people as mentally unwell 'others' prevented people from even considering it for most of their lives.

Also, I do not believe there is an unbalance of trans woman to trans men. Trans women are more controversial (bathrooms) than trans men, which puts them in a public spotlight. Trans women often present themselves as stereotypical women, and if they've not fully medically/surgically transitioned yet, it makes them easy to pick out in a crowd. Trans men, on the other hand, wear men's clothes, which happen to be gender neutral if worn casually. They are often seen as 'butch' women if not fully transitioned, not trans men. You oftentimes probably wouldn't notice or identify trans men when you see them.

Disclaimer: I'm a trans woman.