My guess would be that for non-technical people it's much easier to schedule visible work (frontend) vs invisible work (backend). Are the people that are managing you less technical possibly? If you have a good technical lead they should probably understand the work to give you, but PM's and scrum masters frequently don't understand.

I guess the other thing I'd ask is, why the strong resistance to frontend work? I get not seeking jobs for it or not preferring it, I don't seek those either, but for my own personal productivity I like to have a decent idea how to build a frontend in case I'm waiting on someone that's overloaded in order to deliver my feature etc. It can be helpful for a career if you don't have to frequently tell people "I can't do that", vs, "it's not my strong suit but I can pitch in"