With a TV show they can flush out characters the films would never tackle. I was watching The Gifted with my friend and they were now interested in learning more about Polaris, Blink, and the rest of the cast. The films have focus mainly of Jean, Scott, Wolverine, Mystique, Beast, Charles, Magneto, etc. Maybe its time for others to get the spotlight.
Plus another cool thing Marvel is doing limited series on Loki and Scarlet Witch, but what if they tackled Negasonic or maybe Storm?