You've never heard that GPL can hinder adoption? Most codebases simply cannot use GPL code because if they do, they'd be forced to relicense under GPL (obviously). Not everyone wants to do that, even setting companies aside.

Even people who nominally agree with the concept of Free Software might not want to be forced to use GPL. The freedom to choose how to license one's work is also an important freedom, after all. GPL can be confusing, so you can't fault anyone from not wanting to use it even if they agree with the spirit of the license.

(For the record, I use GPL on some of my projects. I don't hate it, but I also like to use MIT on some projects, too.)