I think the missing piece here is the constant focus on the US.

In Europe ISPs are under much stricter rules about data privacy and generally cannot do things like the above. Having worked for several ISPs here I’ve never found them misusing DNS data (although sometimes it was logged for a time for management / troubleshooting.)

For a European; with reasonable trust in my ISP, I don’t want Mozilla sending all my queries to a US company which can be forced to reveal that to the US govt, or use it for some other nefarious purpose.

FWIW I’ve never used my ISP DNS though have always run my own recursor at home.