If the people are buying directly from manufacturer, why should any costs that Sol-ark has incurred be their concern? They aren't using the official devices, so they aren't enjoying any advantages of that, either.
Why should the manufacturer be concerned you tried to skirt the region restrictions they were very upfront exist?
If Sol-Ark is adding value and competitive differentiation, wouldn't that justify the price premium over the basic Deye product? Especially if Deye is not willing to offer its own support/warranty to customers?
Why does Sol-Ark need to create a more monopolistic landscape? Not being judgemental, genuinely curious. (Well, I know why Sol-Ark wants it. I guess the question is why we allow it).
Your question is really no different than asking why it's not legal for me photocopy books and ignore copyright.
Now, you can argue that country-specific licenses shouldn't be allowed; but they currently are.