I don't want to speak on behalf of AdSense, but there are often good reasons for this.
In the project that I did for another product, we required users to re-enter their payment information to revalidate the account and ensure that the user still had access to the instrument. That process was done to protect the user's instrument.
As I said, I don't want to speak on behalf of AdSense and I'm not familiar with their processes to speak with any authority.
In any case, the change and the reason should have been very well documented and messaged to you (we go through a lot of internal user testing even on these mundane processes). If not, please reach out to the consumer operations team, they should be able to resolve your concerns.
In the project that I did for another product, we required users to re-enter their payment information to revalidate the account and ensure that the user still had access to the instrument. That process was done to protect the user's instrument.
As I said, I don't want to speak on behalf of AdSense and I'm not familiar with their processes to speak with any authority.
In any case, the change and the reason should have been very well documented and messaged to you (we go through a lot of internal user testing even on these mundane processes). If not, please reach out to the consumer operations team, they should be able to resolve your concerns.