Actually one's expectation can very well be that people be nice to you even if you're not using legalese to require that of them.
I wonder how much of an actual analysis is done in these cases, and how much it's just a boss saying that he doesn't want people "wasting their time" working on something that isn't directly related to their stuff.
There'd be some who would change their options and some that would become contributors. Hard to say how it would pan out.
But, when you select a license like BSD (which I've done myself) you shouldn't complain when users don't contribute back.
You selected a license that formally declares your intent and expectations; the user has formally agreed to them.