Upload & Sell: Off
And you're certain all those electronic parts come from a source different from what Nikon uses? Just curious...
They almost certainly don't use anything Nikon. Most companies "own" the tooling for custom boards like this as well as casing, etc. Even contract manufacturers are disallowed from using them outside their contract. There may be other IP issues as well, which isn't a problem in China, will be in the USA, UK and other large markets.
Net: Knockoff guys get a real one and make it with different/cheaper stuff. Their testing and quality standards are generally lower (and often virtually non-existent, though there are definitely exceptions), and they are usually savvy enough to avoid getting tripped up on patents.
(I've worked in the tech industry for over 20 years, a lot of that on the product management side)