> the app is free

I think I found your answer. Even then, paid apps/services still do that too.

In the Play Store, it just says it collects User ID, App Interactions, and Diagnostics, all for Analytical purposes. It doesn't seem like it collects ___location data.

I don't know if they really need User ID rather than some kind of instance indentifier, that's the only somewhat-shady thing I see.

Client IP is city level geolocation. When correlated with user ID and timestamp it gives city level travel history.

Collect enough points and it uniquely identifies a user.