Google has already confirmed that Unknown Tracker Alerts is only compatible with AirTags for the time being, but didn’t specify why

It would seem like the “why” is pretty obvious. Most active iPhones now have AirTag tracking installed on them. That’s not the case for trackers like Tile.

That means Apple has the biggest tracking network right now. It dwarfs the others. FindMy network devices should be the clear priority. They’re more precise, encounter fewer dead zones, and in other words, are likely a stalker’s preferred tracker.

I fail to understand where the "why" comes in. You gave some disparate conclusions. yes airtag is installed on iPhone and tile isn't. So what? Yes, airtags is a big network. Again, I repeat, so what? Are you saying they did the largest network first? Whatever it is, you forgot to state the obvious part of your claim. It definitely isn't obvious.