They did, until the automatic copyright laundering machine was invented. Pretty much every piece of GPL code ever written is now being magically transmuted into MIT/BSD or proprietary code, and the FSF has no solution.
There’s a lot of moral perspective that people apply to this decision, but not all developers have the same goals for their software. MIT is more flexible in its use than GPL, but doesn’t help ensure that software remains open.
Sure it does. The original software will always remain open. It isn't like people can somehow take that away.
The gpl is generally considered to stop at the process boundary. I don’t really understand what you could do with a bsd licensed coreutils you couldn’t do with a gpled coreutils. You could make closed source Linux software which called coreutils in a child process. But by most readings of the gpl, you can do that today.
I suppose a company could fork coreutils and make it closed source, keeping their special extra command line options for themselves. But … I guess I just don’t see the value in that. You can already do that with FreeBSD. Apple does exactly that today. And the sky hasn’t fallen. If anything, it would be a relief to many if Apple’s coreutils equivalents were more compatible with gnu coreutils, because then scripts would be more freely portable between Linux and macOS.