By having homosexuality violently oppressed, ostracized and ridiculed in the past, and slowly reversing that attitude towards it? People were literally criminals for loving people of the same sex...
A lot can happen in 20-40 years, and has happened in 20-40 years throughout history. Industrial Revolution, being a prime example.
We've also become far more interconnected in the last 20 years, which plays a large part - whereas before people may have kept quiet because they thought they were the odd one out they now know they aren't.
I do not agree that the industrial revolution is equivalent to changing sexuality within a society.
I could agree that modern technology and the industrial revolution are very similar. But even with that it has taken 60+yrs for our society to have a computer in the majority of homes after the Manchester Baby was created (and I think this change happened extremely quickly). And, analog and electromechanical computers go back even further. So, again, I think even these things have been a very gradual change happening over many decades once the leading technology was invented.
To further expand on my thoughts, to imply everyone was using ‘industrial revolution’ technology overnight would be heresy. I’m sure it took factories many decades to build and retrofit equipment including a technology run up to the revolution itself. With this said, you peaked my interest in this area and I have some researching to do this weekend.
The sexuality is not "changing" significantly, what changed is that it's getting less dangerous to 1. realize that you are not straight 2. not be straight 3. tell people (including polls) that you are not straight...
And if you go way back in history, homosexuality was totally accepted in places like ancient Greece. It's good that TV series show homosexuality as something normal, because it is. And if it helps to encourage more people to openly come out as either homo- or bi-sexual all the better.