Because 3,000 people died I am unable to just transfer my upcoming flight to someone else? Even if this crazy sentence rang through in any way, just this year I had to fly twice "the next day" so-to-speak and basically bought tickets and then flew the next day. 9/11 is as far from a reason why airline tickets are non-transferable as it gets.

I didn’t make the claim you’re arguing against, that was someone else.

But the answer to your question is: partially

The reason you can’t change it overall is simply airline policy for business reasons. But the reason you can’t change even a misspelling within the last couple of days before a flight is in fact security related.