Because most of us have bitten our nails down to our elbows!
Seriously, I guess as one is working, the thought that the radar picture might suddenly go off doesn't come to mind; much like most pilots aren't sitting there waiting for an engine to conk out. However, what they have and what ATC does not (or did not) is a QRH. Controllers are regularly trained for all sorts of eventualities, but when something untoward occurs the actions taken are largely in the order that the controller(s) involved decide. During my radar training at Heathrow during quiet periods one training officer would put a newspaper on the radar screen and say "Radar's packed up, what are you going to do now?" Not by the book, but very useful.
R/T failure is not so bad - most ATC positions have one, maybe two, standby arrangements so communication should still be possible.