Setup, updates, maintenance, tech support, and uptime guarantees, just to name a few reasons that "the cloud" is better. A service like Wordpress.com or Wix beats the self-hosted Pi on all of these counts.
I interact with a lot of non-technical small business owners and am "that tech guy" in their minds. A question I'm hearing more and more frequently is _why even bother with a website when a Facebook page is much easier and they can see people interacting with it._
Their reasons are not all that different from why many tech savvy HN readers are using a Mac instead of Linux: convenience; less shit to worry about.
Hosting anything on a Pi plugged into the wall goes in the exact opposite direction from what these people want. The centralized services are winning because they pay attention to what the market wants, they build it, and they make it easy to sign up.