It is difficult because having attendants print boarding cards or working with an airport to maintain ticket printers costs money that eats into their margins and increases prices. It's not like they don't warn you that checking in at the airport is paid. I'd much rather save 1€ and check in the way I usually would, even if it means someone who can't read a few warnings has to pay a fee.

Ryanair don’t have anywhere near as many staff at check in, ergo, it’s a cost they save. It’s not excessive, it’s an incentive to do it as they suggest online and keep their costs and thus the total cost of flying down.

Other airlines add excessive charges too, they just put it in the face value of the fare.