Zendaya was a child star on the Disney Channel so she already has a fanbase from that time. She's been able to successfully graduate to more mature roles without falling into the wild child trap that a lot of former child stars end up in. She has also used fashion as a way to maintain relevancy and stay in the public eye and she has a great stylist and a good fashion sense for what works for her. Plus now she's one half of a Gen Z power couple who both seem relatively chill and sweet.

If you want to understand what has led Zendaya to where she is today, I highly recommend The Take's video essay about her.