I never understand why people choose MIT when they create something valuable and don't go for AGPL or GPL. Looks good though :D
Because people these days want to use open source codes freely, without bothering with License. And people who open projects wants their project more widely used. GPL is too restrictive for new projects.
In other words, if you GPL license your code, and someone else uses it, they need to "pass it on" - in other words, their payment to you (and the community) for using your code is for their changes to be passed back to you (and the community).
Code paid for with more code - imagine that.
The only restriction is against those who seek to profit (almost) exclusively off the source code, in perpetuity. They want their cake, and to eat as well. The MIT and other similar licenses allow this - they get to take the code, extend it, profit off of it, and never give back the changes that made the system better (and arguably forked it).
And if you're lucky, you get mentioned down at the bottom of a copyright/license agreement in 4pt font that's barely readable.