It’s everything around the feature that makes it harder: UI design, localization, refactoring, accessibility, state restoration, getting new artwork (for a toolbar button, for instance), dealing with errors, testing, updating the documentation, etc.
If you want to make sure your feature request is dismissed or put at the bottom of the list, make comments about how easy it should be to implement it. Maybe it is easy. But, as Brent notes, it’s likely not so easy and saying it is can be perceived as condescending. – Josh