Because you will be, and everything you see around you has been copied modified and copied again.
Your product can be disassembled and cloned. But there is something that can not be. It’s you, your ideas, your thoughts, your knowledge. Your product is not what others can touch and see today. Your product can not be seen because it still does not exist.
One can not copy tomorrow. If you evolve the product, test hypotheses, learn about your users, you can relax about being copied.
So no need for the NDA, you can open source all your code, you can even give away your client and vendor bases. If this thought scares you, you probably lost already.