I don't believe that being a Lesbian is a new social construct
Oh really?  Why do you think that way?
I believe some women have been Lesbians for thousands of years, but only recently has it begun to become acceptable. Thus, women are able to be more open about their sexuality. 
Yes, that's true.  TI does seem that we're being more open to more sexualities these days
It also can be cultural. Even in 2018, there are still some cultures that still frown on homosexuality. 
That's true.  But at least it's become less illegal.  Society can frown all they want.
Most cultures are based around very close-minded religious practices that are still taught today. It is difficult to move forward when many cultures are stuck in the past. Saudi Arabia just began allowing women to drive!