Buskers and homeless generally gather cash donations in the form of coins. I know digital solutions exist, but they must be they’re relatively difficult and time consuming to organise, and I don’t know how the revenue compares. Similarly, smart phone apps need power, and this isn’t always available. (Nor is a smartphone)
Some adults with learning difficulties can struggle to manage their money. A small, cash, real, physical weekly allowance is much easier to manage than an online bank account.
There are whole other economies that are quite cash heavy (car boot sales, school cake sales, etc) because cash is so simple to use. Setting up card readers in advance would be an effort, and some buyers (eg a small child given £2 to spend) might end up excluded because they haven’t got bank accounts. Just about everyone’s first experience of managing money was coins and cash - I’m not sure you can take that away without losing anything.
Don’t get me wrong, I hate cash now, and I see loads of benefits of going cashless, but I think it needs to be done carefully.