These days it seems that 121.5 gets used all too often for PLOC (Prolonged Loss Of Comms) cases where ATC has to get other crews, with whom they have 2-way, to chase up the guys with the ear wax/wrong freq on their behalf.
If crews stop listening on the #2 box then more instances of PLOC will result in frantic gestures/flashing of lights from fighter jocks that pop up alongside unsuspecting Boeing/Airbus drivers!
Like most of these things, apply a modicum of common sense and what's the problem?