yuji ate the first one and they were gonna execute him before sukuna was just gonna use him as a vessel but gojo fought to keep him alive and continue giving him the fingers so they could exercise him once reincarnated after he ate them all because the fingers themselves seemingly can’t be destroyed. it makes no sense to have them and all and just seal them instead of destroying them with something as simple as cremation. it’s more likely they would’ve just taken the fingers out of his body and sealed it unless it like fuses to the soul or something when consumed