ISP use DNS data for monetization, like selling it to advertisers. There is also a political aspect for many ISP where there is close cooperation with local gov

ISP use DNS data for monetization, like selling it to advertisers. There is also a political aspect for many ISP where there is close cooperation with local government, and the need to comply to request of filtering is pretty high in some countries. A CDN pays ISPs, carriers, and network operators for hosting its servers in their data centers. ISP do this because it provide them revenue and better service to their customers.