There is a story about people getting driver's license having a check box to opt-in into being organ donors, and very few said yes. Once the box was changed to opt-out, very few said no :)
The question is are people saying no because they are privacy conscious, or because they don't care. My money is on latter. In general more people care about Firefox being fast than security.
What's a bigger issue for Firefox is deprecating its add-ons. That's going to hurt its marketshare way more than telemetry data.
There's the answer. And the response? "Tough shit", we'll take away that choice granularly. For our own good, apparently.
Moz has been giving tough shit with caveats for more than a few years now. Perhaps that is why market share is falling?