Really, I think the world would be better if they published more openly and were more open, and I don't think it would really hurt their ability to outsell their competitors at all. Let's say they're working on AR glasses (which they probably are) and Samsung catches wind of this and rushes to market with Samsung AR glasses. How many Apple fans actually think this will make a difference to people in the Apple ecosystem buying Apple AR glasses?
At this point I think the secrecy does more harm than good.