Generally speaking, you can't patent a blade shape or handle shape (at least under US law). The American patent system only covers novel, useful inventions (traditional utility patents) and novel non-functional/purely decorative designs (design patent). Other than pure "art knives" that can qualify for design patents, you won't really have much in the way of protection. Copyright covers creative works, so again, not much help for most knifemakers. Trademark is also very limited, because it needs to be something so distinctive that it's associated with a particular source. In the knife industry, locks are really the primary thing that gets protected (through patents), although logos, model names, etc. are also protected through trademarks.
If you take a design like the Sebenza and copy it, that's perfectly legal. You can't call it a Sebenza (trademark) or use any of CRK's other trademarked IP, but the actual blueprint design of the knife is not protected in any way. SRM/Land make an entire series of knives that are clearly copying the look of a Sebenza, but are branded with their own logos. This is where the line between a counterfeit/knockoff and a legal "homage" is drawn. Ganzo takes a lot of heat around here, but they very clearly do not try to pass their knives off as anything other than a Ganzo. In some cases, they do something I wholeheartedly support: taking features of different knives/brands and making something novel, like a RAT 2 with an Axis Lock.
As to why people care about "homage" knives that use modern designs but not traditional ones, I think it's a combination of things.
- As many have said, the traditional patterns have been around for hundreds of years in some cases, so they've long since passed into the "public domain"; basically, people have been making copies of them since before any of us were born, so it's not a problem; "that's the way it's always been"
- Economic arguments: you will see claims that "legitimate" companies lose out when other companies utilize unprotected IP; that blanket assertion is, given the number of variables involved, very speculative; since most of these tend to be sold on the lower end of the market, it will very much depend on whether the "clone" competes in the same price category as the original; does CRK actually lose Sebenza sales to $20 versions sold on Amazon? No, probably not. Does Ontario lose RAT sales to Ganzo versions at or just below their pricing? Arguably yes.
- Misunderstanding of the law: despite the legal protections for knife designs being relatively scant, some people will look at this sort of copying and immediately assume it's illegal
- Moral arguments: for some, even if they acknowledge that it isn't illegal, they'll fall back to "just because it isn't illegal doesn't mean it's okay"; if somebody thinks something is inherently immoral, it doesn't really matter what anyone else thinks, they're not going to change their mind
- "Value": if you derive personal gratification from having an exclusive, expensive product, that's devalued when someone can get a knockoff for a fraction of the cost of the real deal; a lot of knife enthusiasts participate in areas of the hobby where value and utility are secondary to craftsmanship, artistry and intangible feelings, whereas the general public views the idea of expensive knives as being unjustifiable; in a hobby where the difference in utility is relatively insignificant between a $1000 knife and a $20 version of the same design, and value is largely determined by exclusivity and the presence of details that are generally not obvious to someone who isn't an enthusiast, clones can be a personal affront
- "Geographic issues": a not insignificant number of people in the knife community have very negative feelings toward the place that most modern clones come from...
- Double standards: on its face, this entire discussion is premised on a broadly accepted double-standard; very generally speaking, people are more willing to create/accept a double standard when it helps protect their own views; this is most apparent when people will selectively excuse or ignore IP theft by brands they like but bash on companies they don't like for doing similar things