Part of it I think is that we're still in a period of growing-pains. The web is transitioning from a document platform to an app platform, and until it fully catches up to that mandate, we have to bridge the gap with layers upon layers of frameworks. I think we're entering the downslope of that process, but it isn't finished.
That said, I do wonder why there isn't so much as a proposal for native HTML templating (the <template> tag doesn't count). This has been industry-standard practice for 5 years now and would benefit immensely from a native implementation. It seems like it's well past time to get that ball rolling.