More like many. About 6.5% of US households do not have a bank account. There's also the concept of the "under-banked", which covers people who have them but still use non-bank fiscal implements such as payday loans and money orders. That number is about 19% of US households.

https://www.fdic.gov/householdsurvey/

Poor people have no problem paying in cash for most services.

When an organization does a lot of business using money orders that's a red flag that it's an organization so in the wrong, so terrible, that it can't trust its employees not to skim cash and look the other way when they see each other skim cash.