As one of those manufacturers (foreign), I can tell you that the decisions we make in what goes into the trailer as base, how we build it, what materials to use, and then of course, what price to charge, is a pretty involved dance. What people want, is usually the most expensive, but as you probably know, they don't necessarily want to pay that price. Overland trailers will always be more expensive. The materials and componentry going into them are just more expensive, and typically, the labour time per unit is higher. For example, mainstream trailer manufacturers (Indiana), practically staple that whole trailer together. There's a reason why they implode if they roll on the highway. lol.
As for the foreign trailers, and what was eluded to on here already, is the regulations. There are a couple governing bodies for regulations. First is for the running gear of the trailer. In the case of the USA, that's DOT/NHTSA. The coupler, suspension, wheels, tires, brakes, and exterior lighting, all need to comply with the minimum standards of NHTSA. Even down to how high off the ground the marker lights can be. All of this componentry needs to be certified for use in North America. So, those that make trailers in other countries would need to import these components, and change how their assembly lines might work, in order to install those revised components, and then in turn, import the trailer into the USA. These changes could be a real hinderance or cost increase. For example, changing out their suspension, and therefore the mounting holes. Or having to move a marker light up 2 inches, all change things in their business.
Then there is the safety regulations. CSA/NFPA/RVIA. These are related to electrical, plumbing, and gas. While there are other standards around the globe, and arguably some more safe than NFPA, they are mostly not recognized in the US/Canada. Most dealerships won't sell a trailer that doesn't have CSA/NFPA/RVIA certification. You might have these smaller boutique type dealerships agree to sell them though. But the big dealer chains don't want that liability for selling you a trailer that has a ************ Chinese gas tank regulator or something. It's why Opus imports the trailer, and then installs a bunch of certified components, like the Truma Combi. They are a large enough company to be able to do that.
So, why are there not more foreign trailers? Likely because of the hoops they need to jump through to comply with regulations, and the nightmare of logistics in getting them to North America (instability of shipping costs). Given that the RV market in Europe is quite a bit larger than North Americas, it makes sense that builders over there (even in China) focus efforts in marketing in those countries. I would, if I was manufacturing on that side of the pond. We spent over a year going through the application process to ensure our trailer and building were fully compliant with CSA/NFPA. Major pain in the ass, and pretty costly.
This of course is just me speaking from my experiences as a 'foreign' manufacturer, and what it took to be compliant to import into the USA.
There is a whole other side of things, that relates to mass production versus small scale builders. Anything from China (or made in China and claims to be Australian), are most likely made in huge mass production facilities. And therefore, have cheaper manufacturing costs.
Sorry, i kinda jumped around here, but it's a pretty involved conversation.
