Mostly because their hands are tied by political correctness...
They hired a bunch of dumb people who were hired originally because they
worked cheap. Then made government employees and not allowed to profile as
needed, the rules are also rather stupid. You can not carry a 1" long
keychain knife, but my wife is allowed her 12" long aluminum knitting
needles. I think they should ask you if you have a knife, and if not
issue you one. Everybody with a knife and no one gets far in a hijack
attempt.