Wow, that's fascinating. It really speaks to the utter dominance of Windows over Linux more than anything else. Like even among Firefox users, as of last year, there were an order-of-magnitude more Windows 7 and 8 users than Linux 5.x users.
Don't have any data to back this up, but I would think that the average linux user will instantly turn off firefox telemetry and won't show up on these graphs. It's one of the first things when I install firefox, disable ff telemetry, set privacy mode to strict and then install uBlock. Nevertheless Windows has a huge market share, even if no one turned off data collection, and the year of linux on desktop didn't happen.