tl;dr: Google succeeds when people use websearch. Cloudfare succeeds when people use the Internet in general. People use websearch more when the Internet is fast and reliable. ISPs resolvers are frequently not fast nor reliable. Thus if you can improve peoples Internet experience with a better resolver, you improve your core business.
No need to track anyone via DNS for this to be successful.
tl;dr: Google succeeds when people use websearch. Cloudfare succeeds when people use the Internet in general. People use websearch more when the Internet is fast and reliable. ISPs resolvers are frequently not fast nor reliable. Thus if you can improve peoples Internet experience with a better resolver, you improve your core business.
No need to track anyone via DNS for this to be successful.