My mother youngest brother recently just settled in Manchester. He moved there with her kids and wife. (His wife was a mainlander)
The reason why they move is because he is afraid of the government is going to take his money (which is already limited) He is the rich type in Hong Kong, having over hundred of millions of Hong Kong Dollar in the bank with 4 properties in Hong Kong. But when he move he can only move around 1 million Hong Kong dollar and can't even buy a home in Manchester.
Many people leave Hong Kong because of the same reason, not too many are for "freedom of right or vote" or whatever the Mainland Chinese want people to believe as "Troublemaker"
His original destination was Canada tho, but he can't get the visa to work and took up the BNO thing the UK offered.