For small businesses earning below or around the tax threshold all the charges involved with card machines & digital transactions adds up - it's like a discount on all those purchases vs someone who pays cash. The customer gets no financial benefit, the business loses but the card company gains (they aren't 'banks', they are intermediary companies and they are making a killing, the pandemic is the best thing that could have happened for them).
From my POV I'm a very small food business (below the tax threshold) but am in a location with very bad signal & no landline so CAN'T use a card machine, hence cash only. I did advertise ppl could PayPal but I get charged, every time, & it's just not worth it for me.
It means I pay my suppliers cash-on-delivery rather than monthly invoice which is SO much better cos I'm never in debt to anyone.
For info sake - the bigger machines you see (not the dinky phone linked ones) have multiple charges to the business, not just the transaction fee. You rent the machine, you pay a contract (which you are locked into), transaction fees, the costs of the rolls (which aren't cheap).
The machine breaks, phone line goes down, powercut, banks systems have an issue & suddenly you can't take card so your losing trade as few ppl carry cash to use instead. So they go elsewhere or don't spend at all. Issues happen more often than you think.
So sure, top line as a customer is it's easy to use card/phone. Beneath that line, however, for small businesses there is a LOT going on & it isn't all nefarious 'trying to avoid tax' cos a lot of us dont take enough to pay any. But as a consumer who mostly uses cash I feel like I'm walking thru an airport scanner every time I shop, it's uncomfortable & I feel like I'm being side-eyed & judged. Have had cashiers comment about using cash & feel I have to explain myself - it's pretty horrible tbh.