Ask HN: Why do we never see inovation in web browsers?

I was reading a thread today about yet another Javascript framework. The general consensus seemed to be that a new framework isn't going to make a meaningful impact on productivity. It made me wonder, if there is no more juice to squeeze in the JS Framework world, then why don't we see more innovation in browers? Instead of marginal improvements, what if replace Javascript or html or even http?

I understand today's browsers are hugely complicated, but they didn't start out that way. Why don't we see micro-browsers that fetch some document and render something useful in some innovative way?