Because the simple fact is that their deposits are safe and their records are not at risk from Y2K related problems. All financial institutions have extensive back-up systems to ensure that each night they keep multiple physical records of all account information.
While some members of the public have expressed concerns for the safety of their deposits because they think records might disappear, there is no basis for this type of concern. The safest place for people to keep their savings is in the financial institution that they are already with. Withdrawal and conversion to cash would expose them to a lot of unnecessary risks.