I actually tried to implement a SPA using just ES6 (in Typescript) some years back and ran into quite a few problems with data flow, which frameworks like Vue.j

I actually tried to implement a SPA using just ES6 (in Typescript) some years back and ran into quite a few problems with data flow, which frameworks like Vue.js readily solve. I think that (for example) Vue by itself is quite light (mu Vue apps were never slow, even on a computer that choked on most other webpages). The problem is that many web developers don't care about performance and will hapilly fire tens of HTTP requests while loading the page, which happens to be over 1M because of all the unnecrssary JS and CSS libraries (looking at you, Bootstrap!).