Nothing has "failed" on a technical level. I'm sure if a company hired a bunch of highly experienced devs and said "build us the fastest, most user-friendly sit

Nothing has "failed" on a technical level. I'm sure if a company hired a bunch of highly experienced devs and said "build us the fastest, most user-friendly site ever, everything else is secondary!" you'd get an amazing site. You get what you optimize for. User experience is not being optimized for. The ability to prey on users via ads, dark patterns, info harvesting, tracking and even malware is. This in turn happened because people discovered that, mostly, there are only two ways to make significant money online: 1. Be the first to deliver a revolutionary service everyone loves in just the right form for it to catch on. 2. Gather a bunch of users via some shiny object and then exploit the hell out of them. For obvious reasons, #2 caught on, dominated the web, and will continue to do so until various regulations slow it down.