The transcript of a fantastic talk by Stuart. The latter half is a demo of Portals, but in the early part of the talk, he absolutely nails the rise in popularity of complex front-end frameworks:
I think the reason people started inventing client-side frameworks is this: that you lose control when you load another page. You click on a link, you say to the browser: navigate to here. And that’s it; it’s now out of your hands and in the browser’s hands. And then the browser gives you back control when the new page loads.