Neither of them have been "left alone in their high castles". Both have a large following, are well respected (and controversial), and people have built upon their philosophies or used them to better understand the world.
You can go back as far as the late 2000's and the GPL still had a huge following. With the mobile boom F/OSS was still embraced, but the GPL has steadily fallen to the wayside. You can only be so uncompromising when people need a means to eat.
Now we have an entire generation of CS grads who'll use MIT as their de facto license.