“You never change things by fighting the existing reality. To change something, build a new model that makes the existing model obsolete.” - Fuller

One possible reason is that a truly open web would include things advocates for an open web don't want, such as advertising and commercial interests, or javascript.

Excellent point. I fear many attempts at the open web failed because they were a little too anti-capitalist or FOSS-purist and ignored basic economic realities.