90% of website size is media (images, audio, video, etc). Discounting that and saying that a 1MB page is so much bigger than just the text it delivers is silly and doesn't really make a point. Maybe it's unnecessary, maybe not, but that's subjective and most people would rather have images and decent UI.
It's true that ads are another factor, and it's slowly being solved, but ultimately comes down to the wrong incentives across the industry. The more annoying/heavy ads work better and pay more so everyone from advertisers to agencies to publishers will continue to optimize toward them until something changes (which might be adblocking). This isn't a technical problem so much as business and politics.
However, the publishers these days *are pretty short on tech talent and mostly use off-the-shelf CMS systems like wordpress (which are already bad software) and then just layer on their plugins, themes, and ads to create the mess we have today. Again no easy way to solve that without talent either on the pub side or in the platforms themselves. Some progress being made here with things like facebook instant articles and medium.com hosting.
Overall, the web definitely has a cruft problem, but it's not really that bad considering all the various channels of information access, and it's all slowly getting better.