Few people get paid wages, benefits or pensions in cash. They are paid into a bank account. The government has the Payment Exception Service for those unable to operate a bank account and don't have an attorney. Cash can only be obtained from an account with a Bank card or phone app. The government sees no reason why if you have that mechanism to get cash, that you cannot use it directly to pay for retail services directly, omitting the cash stage. Shops can be cash only, card only or mostly both, but car parks are very variable. Those using cash tend to be either because you can, you are using it to budget, or you aren't comfortable with technology, none of which has to be accommodated by the seller.
First Bristol did a study years ago (2017?), filming the boarding process and found that card payments averaged under 10 secs, where as cash payments were more like 90 secs. On busy double deck routes they could save 1 bus and 2 drivers with cards rather than cash for the same service. Cards had a 50p discount per single for a while to encourage the change over, which has happened.
Tap on - tap off or ENTCS passes, etc are fast particularly as tap off is very often not needed as apart from short hop, the rest is flat fare. Cash often needs 2 hands, so put shopping down, find purse, ask for fare, pay, get change, put it away, collect shopping, carry on.
Stagecoach's trial may be interesting to observe, depending on the details.