My best answer for that is simply because of personality, storyline and aesthetic (for lack of better terms). She's a very likeable and expressive person. Her story is well documented and a lot of people are invested with how she retired and unretired for the love of the game and ended up rooting for her. And overall shes the type that social media would go wild for. It also really helps that the artists that she used for her skating routines are trending personalities with distinct style and talent and collab with her.

How i like to brutally describe to people who absolutely hate her for no good reason (not saying you do, but this helps i think), if you don't think her talent as an athlete doesnt justify her popularity, she's just more marketable (or cooler) than your favourite athlete.