It's very important to remember that Facebook's standardized UI played some role in making it successful. I don't think it would be as successful were it as customizable as MySpace.
You could also define success as enabling many, many people such as my parents who aren't proficient in English or computers and would never be able utilize the internet for communication if it weren't for the standardization offered by Facebook, WhatsApp, Facetime, iOS, etc.
Just like 99% of people want cars with an automatic transmission and take it to the mechanic for any issues, 99% of people just want a tool that gets out of their way and lets them achieve the goal. Whether it's driving to their destination or seeing photos or video calling their friends/family.
If you asked my parents, their goal never was to create anything on the internet, or browse niche websites and learn their layouts. They're not going to learn it in their advanced years, and perhaps they would rather spend their time on other interests they have such as gardening, cooking, etc.
+1 I for one don't long for the days of crappy hard-to-parse pages created by MySpacers and wanna-be web devs on FrontPage. Social media platforms exist because they organize and format information for efficient consumption and discovery. That's the reason they've overtaken Geocities or MySpace.