Piston Broke
How many of your five ground agencies are going to pick up a signal from somebody down in a valley in a mountainous area, eg Alps, Scottish Highlands, or in a Mae West in the Bay of Biscay, Mediterranean etc? You must have worked for some pretty callous companies and/or flown with some callous individuals where guarding 121.5 on Box 2 is not SOP over such areas. Satellites will probably pick up such signals eventually, but only on the next pass over the area, which might be too late. Having made, heard and relayed several 121.5 signals in my career so far, perhaps I can vouch for how important it can be.