When given a blank piece of paper and told to do anything with it, people block. They can’t think of anything. Give them some constraints, a place in their mind for bubbles of thought to form.
A completely open internet is a blank piece of paper. A “Walled Garden” can get people thinking so they can create new and interesting things.
Walled Gardens may be dead ends after all is said and done, but they’re so necessary for creativity, we keep creating them over and over.