Chances are they saw the login as fraud given it went unused via years and the first thing that login did was sign up for YT Premium via a credit card.
A potential problem they're trying to prevent might be where money launderers use google accounts to funnel YT Premium money to specific channels via watch time (since Premium pays out a lot more, and pay per minute watched[0]).
I'm sure they have the best intentions but there's literally no way to appeal it. Why can't they verify the credit card the way every other merchant seems to be able to?
A potential problem they're trying to prevent might be where money launderers use google accounts to funnel YT Premium money to specific channels via watch time (since Premium pays out a lot more, and pay per minute watched[0]).
0: https://youtu.be/Rh5hL47z2us?t=100