Dirge, whys he not picked,

Undying is an outstanding hero and I stand baffled as to why he's not taken for some of the pro compositions in order to take advantage of his impressive early aggression.
Last night we had a random cm game in the queue, a clan friend and I survived the draft and I managed to at least get undying as the last pick to try and control the game a bit more ( our draft consisted of zues, Leshrac, shadow shaman, chaos knight, and undying..not the best picks but the guy wouldn't listen, although picking zues after they picked spectre ended up working out). The other team consisted of a defensive trilane, naga, shadow demon, spectre, OD mid, and miranna long lane.
At the beginning I managed to get haste bot(we were radiant)while the team manages to fail an easy first blood near the rune, I go mid to decay OD several times while basted to zone him out, giving zues a level advantage.
I went too and after my buddy Legion (totally sniped the CK pick) managed to get first blood on miranna (w Ck) I decided decaying the **** out of top was worth it, forced out regen items from all 3 heroes, a net, disruption, and managed to kill spectre before dying myself...reasons I stayed and died: 1. The spectre kill was guaranteed 2. The carry and supports burned through their regen items 3. CK is free farming and has first blood gold to boot

At level 3, I have 2 levels of decay and a level in tombstone, manage to be a bigger nuisance that they can't kill because of my Str from decay, spectre dropped to around 400 max health, while naga was desperately farming and taking big damage from the safe camp. I ended picking off shadow demon, OD and Naga while zues ulted spectre down, CK still farms bot.

This managed to go on for the remainder of a game ending before the 40min mark, spectre was leveled pretty high after picking me off a few times while I was low on Hp, but ended up 6-8 with a lvl1 diffusal blade and treads as the only things equipped in around 38 min..naga and SD were way under leveled, and OD was an impressive 0-9.
So yes they didn't know how to deal with an aggressive undying, and were rather perfect for me to harass being as squishy as they were, but other than that, with the capability to weaken and cripple heroes, a massive damage amplification+slow aura, the zombie house and soul rip deal big damage later, or healing why is he not picked that often?
Such an underutilized hero, well when I play him, call me Captain Clusterf@#k, I play him aggressive and make laning and team fights hell for the other team, anyone else think of ways dirge can fit into a composition and be successful? Early aggression with decay and early killers, makes first blood and more early kills a fairly manageable proposition

So basically, Undying was first pick/ban material a couple of months ago, but he got nerfed(fixed).

The situation was the following, his Decay was dealing the damage before the drain, not after.This basically meant an extra 20(or whatever level the Decay is)damage every cast.Now that thing piles up so hard early game, that it actually made the difference, and coupled with the Tombstone, there wasn't really much escaping.

Wasn't so much that nerf that threw him out of the meta. He was still picked even following that nerf, trends just changed. It got to where trilanes relied more on quick skirmishes for quick kills, rather than slowly bullying your enemy out of the lane with a kill here and there. He's still a very strong laner but people also learned not to underestimate him in early engagements, and if the enemy isn't going to sit there and fight you, you really have no way of catching up to them.