I never came across this narative, that its the only solution. But the harsh reality is that most users don't care, normies will never be good at managing wallets, keys, etc. So custodial is the only way to go for now for most, until something comes along that is more foolproof for the average user... And TBH, for zaps on nostr, custodial is "ok", as long as there is sufficient educating and informing that people should not store their retirment bag in a custodial lightning wallet...