Here in the Netherlands we are discouraged in shops to pay with cash and electronic payment with bankcards is encouraged. So nowadays people dont use/have much cash on hand , simply because they dont need it and its more secure if you dont have any (they cant steal what you dont have)
So its only logical that at assemblies and conventions donating with bankcards is an option. Its secure, fast and simple and everybody has a bankcard with them.
furthermore there is no difference between a box for donations or an atm machine,.. its just the modern equivalent.