But it's not like they put "explosives and other ordinances" in the subject line. For all the bank knew Atta was just some flight school student. If banks were to require justification for every wire transfer, legitimate commerce (also remittances and a bunch of other things) would grind to a halt.
KYC done properly means the bank understands every customer. What you do in life, what you get normally paid for, etc.
Problem is, it’s tricky to do at scale and the banks want to profit more, so it makes financial sense for them to err on the side of caution with small accounts that are possibly net loss anyway (considering maintenance overhead, etc.) but starting with a certain level of wealth I think they are more than willing to not care.
