But the point is that the proprietary code will be proprietary code even if you GPL you just make the company that would use BSD licensed code rewrite it (or st

But the point is that the proprietary code will be proprietary code even if you GPL you just make the company that would use BSD licensed code rewrite it (or steal it since there's no practical way of enforcing it - and unethical company gets rewarded). There is no way to force a company to contribute if it won't/can't. And GPL is all or nothing deal, BSD allows you to upstream selective patches but keep some parts you can't/won't release.