Ah, I thought ICE also required reservations but that's only the case if the train is otherwise booked out (source https://travel.stackexchange.com/questions/72538/what-if-i-u...). For me, trains like TGV, ICE, and perhaps Nightjet make up the bulk of the distance to most places I go, so for me the reservations were pretty much required no matter where you go; apparently not really for ICE then!