European here. I can't even put to words my embafflement upon having learnt that you US folks need two staircases.
Why would you choose to write something here with a snarky attitude like that? There's a reasoned discussion to be had around fire safety regulations, but when you instantly make it about cultures and don't even try to understand, you're not being part of the solution -- you're part of the problem.
That aside, I fail to see any cultural or other reason to require twin staircases nowadays other than ‘that’s how we always did it here’. I admit it openly and state that I’m from somewhere where we don’t do that, and the world works just as well, except buildings have a higher useful to total area ratio.