A cashless society might work well for banks and businesses. I'm not sure that charity collectors would share your enthusiasm. As a society we could also say goodbye to such things as small markets, jumble sales, car boot sales etc. To say nothing of how state-dependent people would operate. How many homeless people do you know that have a debit card? The concept of "embracing change" is a nice soundbite but in the modern technological world we still have cash for a reason.
Moreover, regarding the payment of referee's match fees - it's no big deal for the club sec/coach/whatever to hand the ref an envelope with the money in it. Id take it back home, put it in my wallet, (where it's likely stay for several days anyway) and wash my hands.
The finality of doing the fixture, being physically paid and leaving the venue all within a few hours is something you as a referee are able to control.
Ensuring you're paid (in cash) is something you're able to control before you go. Once you've left the venue, you have literally no tangible control over when/how/if you get paid your match fee correctly. Get back home, wait a couple of days, check your bank - no payment/wrong payment - then what? More time spent chasing/phoning/e mailing club or league secretary. The variables on what could go wrong and the sheer hassle of it are endless.
I am of course just playing Devil's advocate here and the above is the worst case scenario, but not all change is good.