It could still be a case of one person's bloat being another's feature. Though for a website website, the other people could be advertisers, people who develop the site and people who publish content to it. There was a Mozilla report not too long ago that found that just disabling tracking (not ads) reduced page load times by almost half.
In many cases it's not. In fact I've recently worked on several projects where the frontend is stupidly heavy for zero reason. Just sloppy or over engineered code.
I know the full extent of the capabilities - one is just a corporate website with no interactivity. It's just dumb. The previous version was just simple static HTML; but as part of the "responsive design overhaul" it turned into this behemoth that makes several dozen requests to open the homepage. Nuts.
