I've also notice a huge push for youtube premium on mobile. It used to be a once a week thing. Now almost every time I open the app I'm greeted by the popup asking me to upgrade.
The constant unskippable ads in the Youtube app meant I jettisoned the app on my mobile devices and just watch Youtube via the browser (even though they make it a terrible experience) because my ad blocker works in the browser.
I use Firefox to browse and with long click and open in app to let redtube handle it. it also is nice to have the option of watching the vid as popup and keep browsing around on YouTube
Most other companies would have deniability about doing it on purpose, but google probably keeps track of this stuff and runs A/B testing with it etc..