Why do banks ask if you have accounts with other banks?

Question

Whenever I apply for either savings accounts, debit cards, or credit cards, this seems like a staple question for all banks.

Why are they asking if you have accounts in other banks? How do they gain from that?

Edit :

Countries I have personally experienced that ask this : Australia, Philippines

Answer 1

Applying for credit, they want to know what your resources are as part of judging your creditworthiness.

I've never seen the question asked for checking accounts. Best guess I've got is that this is pure marketing rather than anything related to the account application itself -- they want to know whether it's worth trying to convince you to consolidate all your accounts into their bank.