Pig sticker, folding bowie, folding hunter (in comparison to Fox "Special hunter # 648)

[Jjimmii]

I purchased a new Fox # 648 special hunter. A folding knife seems best known as a "pig sticker". I have since seen this knife manfactured by several, mostly German, companies. Most are older knives and are identical in every respect. Every detail/part appears identical to the point looks as they could be interchanged. What's the deal? Why do many companies use the identical design or are the made by a single company branded under various brands? I am a novice and green. Can someone enlighten me?
Thanks!