uh they get denied entry if they are late because german trains often are and it wreaks havoc on swiss timetabling where trains still generally depart to the minute and many commuters plan their day around making connections with a 2 minute change time. if the ICE from basel to zurich is late then switzerland runs their own replacement in its spot and denies entry to the german train to avoid knockon delays.

yes the schedule is full but its not just no space for more trains, more no space for unpredictable trains

The Netherlands should do this as well, maybe DB will then at some point figure out how to run a train on time. The ICEs from Germany are more often late than on time, which then causes delays for other trains using the same tracks.