After few tequila's, and little experience;
A few years ago when I was an engineer on an A-300, Some how, unbeknownst to me, the pacs never got turned on, or, some how got turned off, but at FL300, we got an altitude warning horn. WOW! anyway, before declaring an emergency(mayday) or even a WTF Pan Pan, ole numbskull done figured it out, and with out any rubber jungle, all was well.
Not all pressurization issues are a Mayday!
Let the fodder fly!
Just about the only sensible answer on this thread.
I admit that I don't know all the details but they reported a
pressurization problem not a
rapid decompression, so why all children of the magenta line would declare a mayday and immediately start an (emergency?) descent is beyond me.
A pressurization
problem (perhaps just an abnormal cabin climb rate, or a spike) could be as simple as selecting another pack controller or selecting the outflow valves to manual. However, once a full (emergency) descent has been initiated you're more or less committed to divert as well, because you you probably won't have the fuel to climb back to a normal cruise level once/if the problem is solved.
Obviously thinking and problem solving is not part of a pilot's job these days...