But it's Google. I could name at least 12 datapoints to check wether it's still the same user it was for 10 years on top of my head. Starting with "still using the same device" going to probably things like "typing style", given how sophisticated their AI is.
There is really no excuse for Google's ADD and implementing half-assed features and stopping to support them 2 months later...
This isn’t a feature to authenticate the account. This is to identify the person using the account. They’re tying the person using the account to a phone number that person apparently controls, and thus a billing contact.
This usually means Google suspects you of doing something that might be abusive.
In this case: re-activating a dormant account that was in a data dump would be a safe bet.
Unfortunately, Google doesn't seem to have the best staff. Or even good staff.