The lease agreement on those boxes usually states the customer assuming all risk. Sometimes boxes randomly go missing, and natural disasters can make them inaccessible.

"She sued the bank in Los Angeles Superior Court, seeking $7.3 million. Bank of America sought to have the case dismissed, citing language in its lease agreement stating that the renter “assumes all risks” of leaving property in the box."[0]

[0] https://www.nytimes.com/2019/07/19/business/safe-deposit-box...