I think at some level specialists need to become generalists, or they will get stuck. For a junior backend engineer, it might be okay to not know much about UX

I think at some level specialists need to become generalists, or they will get stuck. For a junior backend engineer, it might be okay to not know much about UX design, front end development, database administration, etc. But at a certain level, you need to know about all the fields outside of your specialization as well. You need to understand why you are doing what you are doing, or you'll end up doing a bad job at it.