You make a real point. My cheque book has not been out of the draw for years. Our dear departed MiL always gave us cheques to pay things which we then shredded and paid on line for her. We had LPoA so this was legal. She was just trained to pay by cheque and none of the providers would accept them.
I took out £200 at the start of lockdown and still had most of it 12 months later. Mind you I am from Aberdeen so that may colour it.

The raising of the contactless spend limit to £45 or higher with ApplyPay etc made a massive difference.
What we may be seeing is more to do with reduction of operating costs.
Retail banking does not make money so anything that can be done to reduce the operational cost and integrate the compliance (laws, risk and security) is king. The more the system automates and guides the less the staff need to understand (I see that a lot when asking for something "different") When you are using the Interweb or phone application you use least resource on the banks side. When you use the phone you also give them a strong identity point they can trust. You have your username and password, you have the phone which has passwords and biometric (finger/facial login) so they trust it is you. The App also restricts the things you can do outside of compliance so protects them from errors you may make.
The moment you ask for something challenging it all goes to pot. I wanted a US$ bank account as the exchange rate was pants at the time and I had some money in the US due to be paid to me. I counted 20+ times they said they could exchange it into GBP for me during the attempt to get the account setup. Every time I said I had already explained this and was getting bored of doing so. Then they would ask again. At least when service was face to face they worked it out a bit quicker and did not continue to insult you. I was told it was due to money laundering legislation. I had been with the back for over 40 years, I had every identity document they requested including proof of tax paid in the US. My final comment was "do you just want to raise objections and offend me or are you here to help me and deliver a service?".
For small transactions I would recommend using Paypal now.
You can make payments with your credit/debit card without having to create a permanent account.
You can set up standing payments.
Transaction costs were less than having a worldpay or other credit card reader (Square is a popular low volume one, many exist)
It is easy to identify payments using comments fields
You can send invoices
You can keep a running list and look back on payments quite easily.
You can embed it on a web page as our glorious leader does.
You can move money out of it to a real bank account in order to receive poor service.
If someone does give you a cheque you will likely find that the app on your phone now allows you to take a photo of it with the camera and pay in on-line. So no trips to the branch (if you can find one) or post office!
I think you can now even bonk your phones together and transfer money using ApplePay and others. Sanitise afterwards of course.