If I had to guess, this chart lines up pretty well with the adoption of smartphones, so I’d say the drop is due to people using the default Android and iOS browsers on their phones. I’ve installed Firefox and use it on my phone but I don’t know many people who bother changing from the defaults.

I also have been paying for Premium the last couple years and I completely agree. I get more value out of my premium subscription than I do Netflix or Max. Plus premium supports the creators more than ads do.