Maybe, maybe not. They'd all do the same sort of cost/benefit assessment and if they deemed the benefit to outweigh the cost of contributing back they would do

Maybe, maybe not. They'd all do the same sort of cost/benefit assessment and if they deemed the benefit to outweigh the cost of contributing back they would do it. 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.