The legal system in the United States is extremely complicated. The national government is not allowed to make certain sorts of laws. State laws govern many sorts of situations. The national laws currently forbid shipping automatic knives across state lines (except in limited circumstances) OR importing them into the USA at all.
There are a few makers of automatic knives in the USA, but they (unlike Spyderco) are located in states where automatic knives are not forbidden. Oregon (Benchmade) does not restrict auto knives. Florida (Microtech) did not, but the Florida state courts seem to be misapplying a quite different prohibition in Florida law to automatic knives and we will have to wait a bit to see how that all shakes out. Some states (e.g., Indiana, where I am located) forbid any sort of contact with auto knives at all so that one may not buy, sell, transport or even possess them. Others may have intermediate restrictions. AFAIK, Colorado, where Spyderco is located, has a sufficient level of restriction that you can't do much with them. I don't know if Colorado is quite as restrictive as Indiana, but it is certainly more so than Oregon is or Florida has been. But even if Colorado were as non-restrictive as, e.g., Arizona the market in Colorado or Arizona would not be large enough to make automatic knives very profitable. Note, too, that Benchmade and Microtech must manufacture their auto knives on site. Spyderco has historically had most of their knives manufactured in Japan, but this would not be possible for automatic knives because then the knives could not legally be imported into the USA. They could sell them in France, but not in the USA.
All in all, the legal restrictions and barriers make automatic knives less than attractive for a company like Spyderco. I can't speak for Sal, but IIRC, he has said that he considers Spyderco knives to be just as convenient as autos and a lot less trouble. Speaking for myself, I could not (legally) buy Spyderco (or any other) auto knives, so I'm glad Spydies are all manual.

(I also suspect that they're a lot more reliable with fewer itty-bitty parts.)
Paul