Because, Webpages have become complicated. Suddenly, you have all this interactivity going on, which you didn't have a decade ago. We went from a series of simple hyperlinked inter-connected webpages to all these popups shoving onto our face, useless fake computer bots pretending to be tech-support and finally big co. tracking every single click, every pixel of your mouse movement. The web has come a long way to support all these.
One of my clients was an airline. He asked if we could track the usage stats of his in-flight entertainment system (just stats, no PII). I thought about it and said yes. Even I was amazed I said because a decade ago it wouldn't be possible. I got it done with service workers (because flight wi-fi isn't a 100% always on connection).
It was a boon for me because I made a lot of money on that project and I needed the money. It's also a curse because every browser has all these invisible code running behind the scenes whether you want it to or not.
I miss those days where everything was just a bunch of tables and default system font-powered webpages with plain blue links. No CSS, no popups, just html and pure content.