I guess, as something pointed out before, that most of crimes are petty crimes which occur to easy or random targets in the street... I'm sure some burglars "would scale the 20 (floors?) courtyard wall like a Batman villain with a rope/hook combination", but they only do if they know what they are going to find inside the flat, if they know the person inside is on holiday or away for the week-end, or easy to immobilise while sleeping (old couples sleeping together, for example)... you don't want to go through all this only to steal a TV or find yourself in the middle of the night in a flat with 4 adults sleeping in different bedrooms who could be armed or hit you in the head from the back with a baseball bat (all of this at the 20th floor of an apartment building).