Where do IP proxy services get 10 thousand residential IP addresses in different countries?

Question

proxy

There are many different IP proxy services. Services in appearance and according to reviews are normal and have been working for years. They offer residential IPs in different countries. Many countries and thousands and tens of thousands of residential IP addresses in each country. Where do they get them from?

Answer 1

Examples
https://habr.com/ru/post/419205/
https://habr.com/ru/post/259177/

Answer 2

take on the black market