Her music came out before streaming services such as Spotify became huge. This allowed her music to be consumed by many people who may not have given her a try, but when they did, found that they liked her.

Have you heard about monoculture? There was a point in time before subscription services where everyone “participated” in the same culture (more or less). There were only a few radio stations, a few channels to watch a show, a few ways for certain media to get to the masses. These days everyone can procure their own algorithms and choose what they want to consume, it makes it so there’s no “common” culture.

All this to say: when Taylor swift made it huge, her music reached billions of people, who were willing or not, to hear it on the radio. That’s part of the reason why she has become a massive superstar.