You may not be able to think of such legit businesses, but they exist. I've signed NDA's at at least two.
Simple reason why you might not want to talk about it: you want to sell to customers on the sly while avoiding creating competition. The product is probably easy to duplicate and doesn't currently exist right now because no one thought of it.
Simple reason why you might not want to talk about it: you want to sell to customers on the sly while avoiding creating competition. The product is probably easy to duplicate and doesn't currently exist right now because no one thought of it.