Authorised Users do not have their own credit limit. They are using the primary cardholder's limit.
True. But it is also true that some credit scores factor the primary cardholder’s credit limit into the authorized user’s utilization. With that in mind, I don’t consider it entirely unreasonable to imagine that some credit card companies may do likewise to establish the person’s credit exposure. Not to mention that the income that the credit card company asks for may be that of the household and not merely the individual.