I don't think that AR-15's and double-edged knives are comparable. To my knowledge there are no national calls for banning or controlling double-edged knives, no politicians railing against them. You don't need an FFL, or a background check to buy, sell, send, or receive a double-edged knife in California. AR-15's on the other hand, have a lot of baggage, both legal and political.
As far as double edged knives, several companies sell them here in California. Back when there were B&M knife stores, double-edged knives were common. I bought a SOG Desert Dagger, a Cold Steel Peacekeeper, and a United boot knife at two different shopping malls. And I've received several from mainstream online vendors (the most recent was a Fox Bellum in 2019 from BladeHQ).
I've never heard of a knife company being sued by the state of California for shipping a particular knife here, much less a knife that is, and has always been, perfectly legal to sell, buy, own, and ship here.
But a vendor is free to make whatever business decisions they want, based on any reasoning they choose to use. But that doesn't mean I'm going to agree with it or support them for it.
In any event, for me it's just an interesting topic of conversation. I have no personal stake in the matter. At least not yet. No vendor has ever refused to ship me a knife I wanted, not even the most evil knives of all-
switchblades!
And believe me, I feel very weird defending the state of California. Usually I'm ranting against it to friends and family
.