I use cash very often; almost always at cafes and restaurants, and often in other places too.

I have several reasons for using cash:

• Avoid surcharges.
• Avoid entrenching dependency on payment-processing companies.
• Avoid easy tracking by banks and payment processors.
• Maintaining a sense of deliberate decision-making with purchases. (Using cash means I physically and necessarily think about how much money I'm handing over, whereas with a phone or card it takes no thought at all.)
• (and other reasons along similar lines and values as those I've listed.)

Really, I think it would be a disaster if cash was no longer widely accepted. Having all transactions funneled through a handful of private companies, with no way of avoiding them, ... that would be very bad for a heap of different reasons. So continuing to use cash simply so that cash continues to be an option is good enough reason on its own.