I am glad you asked this question. I was talking about something very similar with a few of my colleagues recently.
I actually like building the controls that you mentioned on the backend. Building good CRUD routes means everything in life for me (only next to drinking, of course :P). It takes hours to learn how to write CRUD routes, but years to master them.
Let me begin with the boring part - anything to do with the UI bores me (I think it bores me because I struggle do it, since I don't really know CSS). I do not like moving items 2 pixels to the left and 2 pixels to the right. I hope to pick up CSS one day and become better at it, perhaps it will stop being boring then.
I mean no disrespect to the UI community - it's the heart and soul of any application. It's extremely hard to master the UI building skills, IMHO and even harder to find good UI/UX engineers. Luckily, we have some kickass UI/UX engineers at work.