But why?
say what you like about antidisestablishmentarianism; at least it's an ethos
They are Welsh?
I too can say it and I'm very English...ish. LlanPG is a tourist attraction and a great example of an amateur advertising idea smashing it!
That's round 2 of England's established church problems. Not as bad as round 1, where the Catholic church was violently disestablished by Henry VIII so he could divorce his wife. Cromwell told the Catholics they could go "to hell or to Carna". I've been to Carna. It's bleak.
It's hard to disestablish a religion. Too many people believe. In Russia, the Russian Orthodox Church came back after Communism went down. Now Putin uses it to reinforce his rule.
Somebody obviously coined the word as a self-referential joke. And somehow it stuck. That makes it memorable.
Speaking of things that stick... arachibutyrophobia is the feat of getting peanut putter stuck to the roof of your mouth. (I admit I had to look that one up, as it's not nearly as memorable, though I knew the word existed).