Here[1]'s the why:
With the removal of the meatball menu in the proton work, we'd like to move the Take a Screenshot button to the toolbar to allow users to hide it or put it in the overflow menu rather than being visible all the time.???
Edit: Also great to see how they brush over existing users who have pinned the screenshot action to the toolbar, which is something you can do with all page actions (who knew?!).
We had discussed it before as a possibility, but I just confirmed with Romain that it's out of scope.
For reference, ~15k users have screenshots pinned to the URL bar and engaged with it within a 1 month period.
So apparently 15k people did know and now have to manually fix the regression, assuming they know how to do it. I still find it creepy that they gather data this specific, and of course users who disable "telemetry" mean nothing to them, they don't exist.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1691464