The number of people I see without adblockers in the wild is really high. When I ask, most people don't know what I'm talking about or they don't care... that is until I show them if they allow me to.

Most people just want to browse Facebook or their bank and don't have a clue about adblockers, add-ons, etc.

Firefox's Enhanced Tracking Protection seems to serve my needs out of the box enough that I see a ton of nags to "disable ad tracking" on various websites. Why install a third party add-on when the in box tools are sufficient?

It’s possible that people with Adblock are also often disabling telemetry.

I'm guessing, but I would expect that there's a fair few people using ad blockers that have turned off telemetry, and thus aren't included in the report.