(1) Racism, xenophobia, and class prejudice. Knife laws in the USA over the past 150 years have largely been driven by media-whipped hysteria over blades in the hands of various ethnic or cultural groups. I saw a good article on this some years ago:
http://www.knife-expert.com/st-opp.txtTHE LAWS ON THE BOOKS
Nearly every state has knife laws. So does the federal government.
So also do countless cities and towns -- except where the state
legislature has pre-empted this sort of ordinance, retaining a monopoly
for itself.
These knife laws are artifacts of fear -- of prejudice and
uncertainty. If you know a little American history, you can look at a
knife law's wording, and tell when it was first enacted.
* If it speaks of bowie knives and Arkansas toothpicks, it dates back to
the second quarter of the 19th century, to the rapid and sometimes
lawless expansion of settlement in the Mississippi River basin.
* If it speaks of concealed dirks and daggers, it dates to the wave of
anarchist and pro-German terror bombings around 1915-1918, which
frightened an entire generation of Americans into surrendering their
liberty.
* If it speaks of switchblades and gravity knives, it dates to the "West
Side Story" era of the late 1950s, when the mass media drummed up fear
of teen-age gangs, and of violence by immigrant refugees with too many
vowels in their names.
* And if it speaks of school grounds, and "dangerous" weapons, it most
likely dates to the convulsive expansion of puritanical prior restraint
of our own politically correct era.
FWIW, the link above, and its discussion of the original dichotomy between the (often secular) individualists and the (often religious) oppressionists in U.S. history, is a pretty good read, and applies to the gun issue just as much as it applies to edged weapons.
(2) Lack of organized pushback by knife owners. I suspect knife owners tried UK-style accomodation for a long time until a lot of the laws in question were too firmly entrenched to repeal (the ban on self-opening knives being a good example). Knife owners in the U.S. are now starting to get organized and push back, though, and the defeat of the proposed ban on assisted-opening knives a couple of years ago is IMO an early success.
A lot of states do allow carry of a knife on a CCW license, and it seems to me that this would be an easy change to pass in most states.