Because those are important too!
Sure, you don’t need a bunch of fancy whiz-biz or complicated trickery to make things look good. You definitely shouldn’t overdo it either. But putting in a small bit of extra effort into a design aside from just making it look plain good can go a long way to boost the “this looks so sexy” score even higher.
This effort can go into all kinds of things. For example, you can make your drop down menu (which, admittedly, isn’t that great in practice) fall open gradually instead of suddenly just being completely open. Be careful to make it a swift and nonintrusive transition though, we want to keep it subtle. Similarly, make it clear when the user has pressed a custom button by slightly depressing it before making it pop out again.
User interfaces are perfectly navigable without those little touches, but they definitely add to the experience, can make something feel more responsive or even plain faster. They can also help increase clarity of your content, but you should be careful about throwing everything you know in there. The details shouldn’t be in the way.
Subtle business, yo.