Other than the obvious money-grab by the authority (1 million cards x 20 EUR x 1% / 12 months == 16666 EUR income each month), what's the reasoning behind this? Only financially solvent individuals can use public transport?
Fair, per-kilometer pricing. Quoting from the english version of the page linked above[0]:
When you travel on credit, a boarding fare will be debited from your card when you
check in. When you check out, the boarding fare will be refunded and you will be
charged for the number of kilometres you travelled. If you do not check out, you
will pay the full boarding fare.
[0] https://www.ov-chipkaart.nl/reizen/tarieven/instapenbasistar...
Caltrain works like this too, though the card will go $5 negative, so you need max fare - $5 on the card at all times.