It's just about cost. Here's the dark side of the story.
For many sellers, because product exported to US under $800 is tariff free, shipping items one by one to US customers from China is cheaper than shipping in batches to warehouse first.
The latter either means huge upfront tariffs if send directly to local warehouses, or higher rent cost of a Mexico warehouse.
Even if you are dealing with an "American" dealer such as Apos, you are still getting products shipped from China. Some forum members reported getting packages from shenzhenaudio when buying from Apos. That's the main reason.
In Japan this works similarly, except that you usually find packages declare a much lower value, as Japan's tax free bar is much lower --- 10000JPY, which is close to 100 USD. I believe you certainly see packages shipped from China to you that declared only $10, much lower than you actually pay. That's actually smuggling, by definition.
Now say you don't like the product, there are actually two ways. One way is to ask you ship back to China, and they will ask you to declare it lower. Because for China, the tax-free limit is around 50. Declaring original value and the tariff can kill all its profit. So the other, more common way is, to ask you to ship it to a local (Japan) warehouse. By doing so, they still win big, by using you as a carrier to smuggle the product into Japan. So, if you don't like it, they still love you. No worries.
This is how reality works. As a customer, if you get product from China, that's probably new. If you get from local warehouse, it has much higher possibility that it's a returned one.