Being muslim is part of it, with 'it' with a collective identity that quite simply isn't Han Chinese, in a region that the Chinese state is concerned could attempt to breakaway at some stage, both due to a specific set of nationalists, but also a lingering resentment towards the Warlord Era. Allowing any part of what they consider to be China to slip away, whether geographically or culturally, is something they fundamentally refuse to allow. So, they will imprison the Uyghurs. They will break the Uyghurs. They will tear down mosques and they will settle their own to cement their claim to the region, and erase any notion that the land belongs to anyone but 'China', as they define it.