My personal opinion is twofold:

1. they need a diversion. Like a magician (or more accurate a pickpocket) they will take anything to make people blind while they amass their power. It is a sickness of the mind. They are addicted to power and ever anxious to loose it. Minorities are a good enemy for the people to blame the problems on that these people either cause themselves or dont want to take care of. In the past it was witches, nowadays it is other minorities.
2. minorities have been fighting for a place in the world for a long time and there have been significant improvements. But that is not a positive development if you want to rule supreme. If you‘re power crazed, you need people to fall in line. Otherwise it wont work. We have ample evidence that only a sufficiently subdued population will not rise up against authority.