Yes, it does seem strange. I think it was David_42 who explained it well. The jist of it was that the temperature at flame out (boiling) and then cooling is enough to extract the aroma and flavor that you desire from this hops addition. The longer times (over 20 minutes) extract the bitterness, and then the lessor times extract more flavor/aroma. That is why you often do the additions at 60 minutes, 15 minutes, 5 minutes, 0 minutes. You get different things from the different additions.