Because I like giving people the freedom to do what they want with the software. GPL carries a copyleft and it bundles a particular philosophy. I'm a bit more libertarian. It also allows for profit firms that want to extend the software for their own products to collaborate on the main codebase.
This is a really old fight since the days of Stallman.
Hmm, I do see your side of it.
I'm rather neutral, with only a light favoring towards the GPL. I suppose that you need to do what works for you. Software should be fun to write. It's wizardry.
Not a political tool. Or at least it shouldn't be.
That's precisely why most of my code (including piston, python-graphene and python-steem) are MIT licensed.