I think its completely natural after a very dark time for humans to swing the opposite way and become light-hearted and facetious, as happens in X2.

If you look at history of last century eg, after World War 1 there were the 20s which was a fun time at first. Also after WW2, the 60s were kinda wacky (ok after a 15 yr gap when things were a bit grim, but then that war had literally destroyed much of the civilised world).

In Spira they were rebuilding Kilika just after Sin destroyed it, so pretty resilient there!