It is not simple to make something simple.

In fact, making a complicated thing seem simple takes time and patience to accomplish. Handing a team a complicated problem and the directive, "Make it simple." will likely lead to disappointment. This is especially true if that is the only directive you give them.

It is users of a system who are best equipped to tell you what's simple. If you are designing a new system it won't have any users until you're ready to show someone something.

That isn't a Catch-22 unless you make it one.

This is front-of-mind for me because I am using Ghost and it is simple. But would it be so simple if it weren't for it's forebears in the CMS and blog world?

This in no way diminishes the achievement - being able to see how to make something simple, and deciding to do something about it, is not something everyone can do.