Do you have a source on a country that legalized gay marriage without social networks? I’m not saying it can’t happen but that would put a dent in my theory. I think Taiwan had it happen before FB but they have what I would consider social networks before we did.
Taiwan was very recent - 2019.
I'll grant that none of these were before the internet but there's nothing uniquely special about gay marriage that required the internet for organising, a huge amount of activism was done in person, just like in various other civil rights movements in assorted countries pre-internet.
So I might still have a point?
Same thing if you think about the #metoo movement, all it took was a tweet for the world to start moving, whereas it took a woman to kill herself in France in 1944 for women to get the right to vote.
[1]: https://en.wikipedia.org/wiki/Same-sex_marriage#Timeline
1. China 1,394,015,977
2. India 1,325,349,639
3. US 329,484,123
4. Indonesia 272,856,400
5. Pakistan 233,431,156
6. Nigeria 213,986,428
7. Brazil 212,041,332
8. Bangladesh 162,532,538
9. Russia 142,588,206
10. Mexico 128,840,997
The thing that matters more is GDP/capita