Martini - the airspace/airfield structure here in the USA often allows me to do PFL's into airfields (without warning to the victim - err, sorry - - student) - and providing a suitable touch down area is achieved then I feel some value has been gained.
Much to my disappointment though - a large number of schools here (both private and "academy" level) have a mandate that you will not land their aircraft on grass runways under any circumstances.
Short field and soft field take-offs being limited to 5<10 thousand feet tarmac runways. Makes a joke of the whole thing. The idea of a PFL to land into anywhere other than a fully prepared strip would be outrageous to the schools - and with the authorities requiring fire/ambulance cover within three minutes of the alarm being raised, I doubt you would fare well if you had an incident whilst doing as you suggest.
Trouble is - I full agree with you. There should be more landings.