I mean, the non alarmist view here is that they are planning to use data provided by the various stores (Steam, Epic, etc) to determine installation count.
Not defending Unity, I haven’t done enough research to have an opinion on the change; but this take seems to correlate two things that probably aren’t related. Plus, what’s easier to do: build a system that tracks specific installs of specific games to specific hardware or to ask Steam and Epic for install counts over the last X months.
None. The beauty of a federated system is that I can stay in my home and still interact with all of those groups should I choose. If using the local function is important to you, then whichever community you are interested in.