Well, I think it had to do with bringing that stuff in-house. As far as I know, Netflix cancelled the Marvel shows because of
Disney+ being competition. That, plus the re-org of Marvel Television, which had been a seperate division under Jeph Loeb, meant Disney saw the opportunity to move in a different directiion with TV & streaming. When they bought Fox the now had the X-Men rights and naturally wanted them as part of the MCU. Considering the previous series was somewhat imcompatible and that the last few movies had not been well received, they quietly killed it in favor of a reboot. Honestly, those Fox X-Men movies aren't very good, excepting a couple. They don't hold up well at all. I always liked the first one, and First Class is probably the best film in the series. The rest are mediocre at best with many being flat-out terrible or even nonsensical. I think rebooting them into the MCU is the smart movie.