How to gain investors' trust if for security reasons you can't open the information about the project owner to the public?
By simply building a good product/project. So people judge the product, not the owner or developers. And within that scenario and in the cryptocurrency world, decentralization should be encouraged, hence its characteristic is tied to the product.
Kindly look at Bitcoin, do we know the owner? Nope. Do people still invest in it? Yep. And as we should have known the saying, don't trust, verify!
What organizations are there that provide KYC for project owners?
IIRC, there was some project that solve owner identity verifiability for its users with the owner's privacy in mind, but I forgot the name. Nevertheless, I don't think there is a point in it. Back to the reason above.