Wordpress takes a simple thing (One-way flow of text from author to reader) and makes it easy. It could be a lot harder to deal with something where information was going both ways.
A very important part of an interactive webpage is how it changes over time and with different inputs. Web developers have no trouble looking at some example widgets and imagining all the possible things a user could make them look like, but most people (might) have trouble doing that.
The same thing, I imagine, applies to running servers. I only know a bit about operating servers, but from my experience there is a complete, unremovable complexity that comes with having a powerful set of tools. Perhaps, we could remove almost all the configurability from the instant-server kit, but then why would you want to run your own?
Wordpress.