Either there is not much consideration given to usability of the product or it has now so many bells and whistles that simple things are not simple any more.
Consider for example...commenting on some piece of text. Confluence has all sorts of restrictions on what I can select and comment on. I am sure your R&D has 100 explanations for why that is the case or why it should be that way. That does not matter. In the end it's just plain annoying to the users and wastes lot of our time as we need to find another piece of text to place our comment on and then explain that our comment is about that other piece of text. Imagine doing that all the time...
Then there are very basic bugs. For example, you select a piece of text and then try changing the format to 'Header 3', it changes the previous line to 'Header 3' no matter how I try!