Atlassian recently stripped the wikisyntax editor from their wiki, forcing the editor to be a newbie-friendly WYSIWYG GUI that's not really WYSIWYG (it uses a lot of incorrect size placeholders). Thing is, it is easier for newbie users... but the data structures are insanely more generic and it's much harder to make the data on your page fit in a way that's consumable for the reader. Worst of all, it doesn't handle old wikisyntax pages at all well, so if you need to update an old table, it can cause problems.

A good GUI editor is one that produces good output - and that is really hard to do, particularly in the constrained space of a webpage.