User blog comment:KillRoy231/Bobby's deal with Crowley - Plot hole/@comment-74.132.82.188-20180717165611/@comment-1031724-20180718003654

Well when Gabriel put Sam in the time loop and Dean stayed dead for quite some time before rewinding it, Gabriel said Dean was in hell. Besides, I think Azazel killed John himself after their deal. So, usually it's traditionally Hellhounds to do the killing, thus "collecting" the souls that are doomed for hell on death.