I don't think they are being arrogant/insufferable. If they are singer/songwriters then they don't really need the help from songwriters, they just need producers/marketing help. (of course they might have co-writers but it's normally people in their inner circle). So I would be confused too if people sent me songs to sing and I'm like uh, I write my own stuff
that's cute though that Lorde said same haha.