I think what you describe is a side effect of the "move the Web forward thing". I see the motivation for moving the Web forward as a cost-savings measure for software developing companies, which they believe will be achieved when "write once, run everywhere" is achieved. This time that particular Holy Grail is thought to be achievable through browser-based development. They essentially want the browser to become something very like a full VM running on a host OS. The natural consequence of this is increasing complexity.