This is one moan to far, if you're outraged by this there's no helping you.
If it was your local supermarket or something then yeah, but it's a football ground, there's about a half hour period, bit before, and during half time, where you are likely to buy things. The most important thing is speed, contactless takes a couple of seconds, removes you counting cash or looking in your wallet, and removes the person serving counting change.
I don't get the "poorer people don't like contactless" comes from, I'm a poorer person (poor as balls m8) and I use it exclusively unless someone gives me real money for some reason, but my money is all spent online or with contactless payments.
People act as though 30,000 people are going to inconvenienced and we should revolt, but really, probably 50% don't even buy anything in the ground, and 45% don't give a toss and are quite happy to use contactless like they do everywhere else in the world.
The prices are the issue, not the form of payment.