I am far from an out and out Taylor defender, but I think it boils down to the fact that her lyrics touch on a lot of universal themes of girlhood and she actually does write a pretty good hook/earworm (who else is going to make make a lyric as simple but also stupidly relatable as "its me, hi, i'm the monster, it's me" with a little melody that will get stuck in your head).
Her other weaknesses as an artist make her more relatable, which I think is obviously endearing to a lot of people. It's easier to sing along to her songs because her vocals aren't crazy good etc.
Beyond that... full credit for working her ass off and meticulously maintaining her image every step of the way.
Give me Olivia Rodrigo any day of the week tho.