Because you are and that's not a insult: you started this thread as 16+ hd player and I doubt right now you are a 2k+ voobly player (or even a 17/18+). Accept that you are a pleb like most of the people in this thread (me included)
He's 19xx on HD now, and would be roughly 15xx on Voobly, give or take 50 elo or so, based on my direct experience of 5 games of varying length with him. Just an opinion, no complex maths required.