Because that's a false dichotomy. Corporations will always prefer BSD code to GPL code. But there are many examples of corporations contributing GPL code to GPL projects. If the same projects were BSD licensed, then the corporation might have just forked them and their improvements would then not have been made widely available.
You just gave another false dichotomy. Just because a corporation looks to use BSD licensing doesn't mean it won't contribute back. You're attempting to derive intent from a license choice. It's not that simple.
No, I didn't. Notice how I used words like "might", implying that the scenario I described is but one of many plausible scenarios.
Certainly corporations contribute code to BSD-licensed projects. But equally certain is the fact that some corporations contribute code to GPL-licensed projects when they otherwise would have kept their code to themselves if they weren't legally compelled to open it.
