The MIT license guarantees that businesses will use it because it's free and they don't have to think about releasing code or hiding their copyright infringement. The developers I've seen using that license, or at least those who put some thought into it, did do because they want companies to use it and therefore boost their credibility through use and bug reports, etc. They knowingly did free work for a bunch of companies as a way to build their CV, basically. Like your very own self-imposed unpaid internship.
The GPL license is also good for developers, as they know they can work on a substantial project and have some protections against others creating closed derived works off of it. It's just a bit more difficult to get enterprise buy-in, which is not a bad thing for many projects.