As a rule the powerful (whether individuals, groups, countries or civilizations) do not change until the wheels fall off. It's not their portion to adapt; the rest of the world is required to adapt to them... until the wheels fall off.
A big reason why even gun-enthusiast countries like Australia, Finland, Switzerland and Canada have strong regulation is the absence of a moneyed interest in promoting social distrust.
It's not madness at the individual level; it's the madness of America becoming a society that hates and distrusts itself first and most, has become armed to the teeth against itself, shows every sign of being not just on the verge of civil strife but has a small vocal and well-provisioned segment that is fully resolved to do so, and to hell with the consequences.
Where did these terrified and terrifying people come from? I woulds say it's culture from many angles; we have been encouraged to distrust one another to a level that unsurprisingly makes the weakest-minded, best-armed among us crack first.
What these shooters do is monstrous and properly reviled. Yet what they are even more than monsters is canaries in the coal mine.