Interesting! I was about to ask that question in the feedback thread so answered nicely. Ask for ticket, passenger response, “You expect me to pay for sitting on those hard seats?!”
If you ever have been transported and sit in one of the "Silberlinge" you would understand ;-) The open ones ( not the 6 person compartment ) was like sitting on a wooden bench.
Oh yes, visiting Germany in the early 1980’s I had the dubious pleasure of travelling in the Silberlinge and similar byl coaches several times. Though nothing compared to 11 hours in a Bm232 UIC compartment from Hoek Van Holland to København. Not just hard plastic but the back cushion didn’t even extend up the compartment wall! I still don’t understand to this day why DB and many of the other European railway operators provided such uncomfortable experiences travelling second class, often long distances compared to the UK or Scandinavian countries where you had nice reasonably comfortable cloth upholstered seating. Maybe it was for cheapness, maybe easier to clean but it wasn’t very comfortable and a culture shock when first stepping foot in Europe!
On modern German regional trains, the driver operates the doors, and the guard, if there even is one, only checks tickets. That includes not just all the EMUs you mentioned, but even the Dostos. If anything, too many German trains have Guard Mode, not too few... On long-distance trains, the guard plays a part in door operation, but given the few stops, they aren't great for guard mode either.
