Few German stations have barriers. It's actually "profitable" in most cities to never buy a ticket, checks are rare. I guess German mentality helps avoiding widespread abuse (and the fact that it's a crime under German law).
In SF you can simply not pay,there is no control. In argentina, the bus driver might not start the bus if you don't pay, turning the whole bus people against you. In germany, you get a damn ticket very fast, which you can pay with credit card.
I once didnt pay the ticket and felt like Jason Bourne.
Damn. I really was like Jason Bourne.
StGB means criminal law.
(1) means that using public telecommunication services (eg. public phones, maybe paid public wifi?), public transport or entering an event with the intent not to pay the fee can lead to jail up to one year or a fine, unless there's another law that mandates a bigger punishment.
(2) means that even the attempt is a crime (ie. you don't have to succeed), otherwise them catching you would make you exempt from that law (as long as you paid up).
The first few incidents can usually be settled with the fine set by the transportation authority, both to avoid too much work in the legal system and because you might legitimately forget it every now and then (and that means no intent = not criminal = they'd lose a case based on this law).
After too many occurences they'll claim that you can't forget it that often, which helps build a case in court.
Not to mention that the way to pay for cash doesnt give out change, which means taht if you dont have a clipper card, you just dont pay anything at all.
The operators are adjusting this so that there are just enough controls to have enough payments. This is an optimization problem and they know what they are doing and how much.