I'm sure that when ICE trains first came out they were reservation compulsory but I may be wrong.
DB never had a compulsory reservation policy, except for peak DB Sprinter trains, but that’s gone too. Obviously, on international services, in other countries their rules apply, which is why an ICE or THV train to Paris will be reservation-only from the border (but not for domestic travel!).
I believe that DB are right. Germany is a decentralized country meaning that not everything tilts towards Berlin. Typical journeys are therefore not that long, motorways are excellent and many Germans have their BMW or Mercedes parked in front of their door, meaning an alternative is easily available if the train is not user-friendly.
Germans actually do reserve a lot and many trains are fully reserved. The important thing is the extra flexibility if plans change - you might have to stand, but you still get home.
Interesting, the same nonsense as here then. Wonder who did it first?
I think it actually is a very good idea. It’s a clear message that you will likely not get a seat and travel at the risk of standing. So if you can, you will chose a different train.