Why is account A set to not be able to read the information of customer B, but can check the consumption records of customer B?

Because the permission setting of each major function (customer, consumption, etc.) in the system is separated, if you want allow account A to read customer B's information and view customer purchase records, then the system administrator need to set both permissions seperately.

If you do not specifically set permissions for account A, account A will only be allowed to see customer B's consumption records, account A can only query consumption records, but cannot view detailed customer information.