Yes the Brits. are a pain in the ear with this archaic practice of practising on 121.5.
There are numerous reasons for pilots to tune VHF2 to 121.5 for silent monitoring aside from a possible "mayday relay" or notification of ELB signals, including having a second common frequency to allow ATC or other aircraft to contact you on to provide timely notification of an unnoticed failure of VHF1 or mistuning of com. frequencies.
Manys the time in busy European airspace l've heard ATC chase up and locate an aircraft on 121.5 that had missed or misset a frequency transfer.
The rest of the world seems to be able to train and nurture perfectly safe and competant pilots without this need to continuously practise on 121.5 so whats wrong with the UK.