The X-Men are some of the main faces in the Marvel Universe, but they've yet to officially debut in the Marvel Cinematic Universe. This was mostly due to cinematic rights, but now that Marvel Studios and Disney own the merry mutants, fans have been eagerly awaiting their introduction en masse. The shared universe seems to be slowly building toward their presence, and inverting the usual superhero movie norms can actually further build up hype for the X-Men.
Source：https://www.cbr.com/brotherhood-of-mutants-setup-mcu-x-men/
