Problem is those millions will still be using Google Services, just on a new phone paid by themselves.

Not necessarily. Every time you force a user to abandon their current product you risk them looking over the wall at your competitors. In the U.S. at least, iPhones are really attractive, and I say this as an Android user. When my Pixel 3a is EOL'ed in May 2022, I think I may take the plunge and finally switch. If I do that, Google immediately loses my valuable telemetry, they lose my usage of Chrome mobile, and they risk my switching to iCloud - something I can't use on my Android phone.