First, as you already paid yourself for most R&D expanses and came with ready to manufacture solution.

Next, as each plastic form on special equipment modification is very expensive, usually more than $10000, complex plastic molding form can be easy $50000-100000. And if you are not big you won't use it's resource or it will have remaining resource with more imperfections. Plus it is much more simple for same people to make second same form :-). Same if fully true for PCBs and so on.

Another thing - some of top management workers will try to share information and schemes with their partners at similar factories. As in return they get similar reward :-)

Hence, if product is nice and you are not big and important client - you will get copies appearing in the internal market quite soon. And you can be sure that it will be offered as option to all small domestic brands who make rebranded products on Chinese factories.