Originally Posted by
Ready2Go
This has nothing to do with airport design; it's because you've been in contact with checked bags, which may contain many types of items that aren't allowed in cabins. You have to be screened in order to ensure you aren't carrying any such items.
Actually, it does have
a bit to do with airport design. If you were carry-on only, you wouldn't have to be able to come in contact with any checked bags
if there were a separate routing through Immigration/customs for you (which didn't allow access to the checked bag area), but I've not seen such a separate Immigration routing for carry-on-only passengers at any airport in the USA.
It's only because they lump carry-only people with people who check bags that you're not "sterile" after going through USA immigration on USA soil.
There are ways to clear immigration and stay airside, if you're carry-on only, in some airports overseas.