I think what SabenaBoy is saying.
Listening to 121.5 over Europe is distracting to the primary job because of all the rubbish that people say on it. Leaving Europe it gets a lot quieter and you are more able to listen.
With modern ATC suites, surely it wouldn't be that technologically difficult to add an option to the screen to bring up a SELCAL option to call an aircraft. After all, if a geek can program a smartphone app in a few hours, surely a function could be dropped on to your systems? I can however see the future of this in CPDLC instead.