You will find those shouting the loudest that "cash is king" and using those who are disabled or elderly as the reason are mostly business owners who like cash not going through the books.
Cash has been supplanted by more convenient ways of paying and as time has gone one and the tech to take card payments has become cheaper, it makes sense to those businesses who are not trying to dodge tax.
Lots of legitimate businesses (around here, certainly) still process quite a number of cash transactions and I don't think it's very fair to suggest that they're all avoiding tax. While there are probably a handful of businesses out there that are dodging tax, don't tar them all with the same brush.
Both my local pubs now happily accept card payments and the one that had the £10 minimum spend seems to have dropped it. Even though contactless has been around for a good while, it only really took off here at the beginning of the pandemic. Even then, the older folks who come in are still very much cash only. If I'm out for the evening, I'll settle my bill and pay with contactless at the end of the night but if I'm just out for the odd pint or two, I'll pay by cash. Those transactions go through the till the same way.
I still use cash for parking - it's far quicker and easier than having to check which app they use and go through the faff of downloading it, putting card details in etc.
This is not the gotcha you think it is..
You forget that they cant accept cash either when the systems go down. The managers wont take the risk of money going missing and it messes up stock levels as most tills are tied to the stock and ordering systems.
(I used to work as a manager at McDs before we took cards . If the till system goes down you would close.)
I worked for a large supermarket some years ago and if the systems went down we'd still process customers who were waiting at the checkouts. It'd usually entail estimating the value of the goods in the basket or trolley and agreeing a value with the customer. Cash transactions would still be processed, cheques would be hand-written by the customer instead of being printed (we still manually wrote the guarantee card number on the back then anyway) and fall-back card machines (the ones that took an imprint of the card using carbon-paper slips) were located at every till. There was no way to authorise these online and they'd be processed manually in the cash office.
Stock control systems would certainly be out of kilter for a while and there would undoubtedly be financial loss, but the thinking was that it was better take the hit and get those customers out of the way than to have to deal with a load of abandoned trolley-loads; it'd be too time consuming for staff to put everything back on the shelves and anything that was chilled or frozen would have to be wasted because it wasn't certain how long they'd been out of cold storage.