I think I remember reading it in the FAQ, but I can’t find it now. It looks like the Redox book used to have a chapter called “why mit” but it’s not there now.

Preference for MIT and Apache is part of the culture of rust. Also, the lead dev behind Redox has mentioned that he chose MIT over GPL because it makes it easier to contribute, which he felt was important for getting Redox off the ground.

GPL was the most popular at one point. MIT overtook it around the turn of the century, I think.