Most users don't notice any real differences vs using their ISP DNS, and seeing it up and configuring it is yet another thing to take time or go wrong.

We had edge delivery issues when I didn't use my ISP's DNS, especially from Apple. Not exactly sure of the mechanism, but downloading Xcode would take 2 hours instead of 10 minutes.

Comcast doesn't let you change your DNS unless you run your own router. And they also rate limit you if you do.

"You relied on a service you pay for to actually work? What are you, stupid?"