Why do banks require a copy of a long-expired visa for account verification?

A user reported that their bank (SCB) requested a copy of the visa they held 15 years ago when they opened their bank account, which they found unusual. Other users chimed in with similar experiences, especially those who applied in Cambodia, noting that they had to provide documentation related to their past visas. There was some confusion and frustration expressed regarding why such an old visa was necessary, with suggestions of providing letters or alternative documentation to clarify the account's opening details.