> even if cash is legal tender and they, by law, _have_ to accept cash
this is not true as it is not what "legal tender" means. Legal tender is something that the government must accept as payment, not private enterprise.
> Businesses don’t have to accept cash.[0]
> There is no federal statute mandating that a private business, a person, or an organization must accept currency or coins as payment for goods or services.[1]
[0]: https://www.accc.gov.au/consumers/buying-products-and-servic...