But do they do it whether you're logged in or not?
I noticed the ChatGPT app also checks Play Integrity on Android (because GrapheneOS snitches on apps when they do this), probably for the same reason. Claude's app doesn't, by the way, but it also requires a login.
You don't need a phone number to create a google account. (Though the account creation flow is inconsistent in this, in sone situations it will require a phone number, in some it won't.)
I noticed the ChatGPT app also checks Play Integrity on Android (because GrapheneOS snitches on apps when they do this), probably for the same reason. Claude's app doesn't, by the way, but it also requires a login.