Anyway, there is a difference between sharing an idea and sharing all information during development process which might include sensitive and costly R'n'D things, and that's what my point is about. If it wasn't like that, and sharing everything was always beneficial, we would see a line of developers willing to share everything they do with community, but that doesn't happen. Instead, companies compose NDA's for employees and focus test users, and put protective film on office windows, keeping development in secret up until a certain point.

It's big companies that do that. I work for a small company (I work on Factorio actually) and I'm not bound by any NDA whatsoever.

The point of not sharing everything with the community is that rumour has a way of spreading and starting a life of its own. You say “Oh, I'm working on X” somewhere public and a week later, there's a Reddit post saying “the devs have confirmed that X will be in the next release”. Then the feature gets removed and everyone loses their mind saying “But you promised us that X will be there!” That is undesirable. Although I suppose this is only a problem when you're working on a game that already has a community – there's less danger of rumour starting a life of its own when you have an audience of three people.