Also all the tracking and analysis tools that are integrated in most ecommerce are huge. We made a website for a company that was really fast and snappy. Then they added all their tools and it turned into a slug.

Prioritizing developer experience is not the reason we use front-end frameworks. People expect the web to work like a desktop app (no page reloads). The initial request might take a little bit longer, but in the end a well written front-end app will feel faster.

The problem is that people don't worry about bundle size and cram every library off of npm into their website.