When do you have to explicitly close the flight plan? Only on airports without ATC/AFIS? I made about 20 IFR flights in Switzerland and southern Germany and never closed the flight plan explicitly, it was always done by the controller. But these were all flights to airports with TWR, is this the decisive factor?
Even at fields with “only” an active AFIS, he will automatically close the flightplan for you, without asking. Soyes, you only need to do it yourself is when neither TWR nor AFIS is active.
Thing is: in Germany for example, the AFIS concept doesn’t exist. We have the “Flugleiter”, and depending on a few factors, some of them will close flight plans for you without asking, but many won’t. It’s not their “task”.