To the idea of how Taylor Swift got so popular, I've had a general theory lurking in my head. I briefly dated a girl who moved to the west from China, and she had basically no pre-prior North American culture knowledge, since she was no westaboo and just moved to North America for the better life outcomes.
Anyway, so she got a car, and it had that fancy Apple Carplay integration, and she started using Spotify as the radio in the car (never having used Spotify before).
Well, Spotify just pushed Blackpink and Taylor Swift (the old hits like "You Belong with Me") nonstop to her, and it formed her music tastes for her. So suddenly a random Chinese girl whose prior music preference was entirely Chinese music was now a big Blackpink fan despite never being into Kpop before, and she was a fan of Taylor Swift.
I think that happened with a lot of women. I've never used Spotify because I'm autistic as fuck and the idea of Spotify and your lack of full control always seemed stupid to me. But I know I'm in the minority based on coworkers (since all my friends and family share my autism).
I haven't explored this theory too much, but
random reddit posts have examples of people noticing Taylor Swift's music being pushed on them in Spotify.
As an observation, the musical theme of the songs that were pushed to the girl I knew all revolved around a general concept of "I want love / I want you boy / stop playing and love me" (As if it's your last by Blackpink, You belong with me / Love Story by Taylor Swift, etc).
And that theme really resonated with her, and I'm sure it's the main resonance with "swifties" given its almost entirely females within a certain age demographic. I'm sure there's a much deeper thought exploration on this, whether it's because of feelings and desires mostly felt within a certain age, or whether it's because of cultural experiences and changes the older demographic wasn't privy to. But I digress.
TL;DR Spotify has pushed Taylor Swift onto countless NPC women who latch onto her due to their lack of agency otherwise and the themes of her music resonating with them