Gerry. Yes I agree. If no calls are answered I would have to rely on my ELT. But as I have explained -extensive testing I have done over a number of decades in some very remote places in this world show that 9 out of 10 times a pilot will get an immediate answer by calling on 121.5 .
If more GA aircraft monitor the frequency it will be even more likely to get a reply.
And as mentioned ATC can contact a VFR pilot they may have inadvertently flown into controlled airspace by requesting an IFR aircraft that is already on an ATC frequency to call on the 121.5 guard frequency. That's the reason the FAA has this 121.5 requirement for VFR aircraft.