I completely disagree Jaco, Hangarback Walker is great in Legacy. It's not played in Legacy because no one creates decks and takes chances in Legacy. The player base is downright terrible compared to the brewers in Vintage.
Here is a list I've run with great success in Legacy. I don't play online and I don't travel.
http://tappedout.net/mtg-decks/11-09-15-affinity-legacy/4x Ancient Tomb
4x Arcbound Ravager
4x Chalice of the Void
4x City of Traitors
4x Cranial Plating
2x Crucible of Worlds
2x Darksteel Citadel
4x Hangarback Walker
4x Inkmoth Nexus
4x Lodestone Golem
4x Memnite
4x Mishra's Factory
4x Mox Opal
4x Phyrexian Revoker
4x Steel Overseer
4x Wasteland
sideboard:
3x Coercive Portal
3x Grafdigger's Cage
3x Surgical Extraction
4x Thorn of Amethyst
2x Umezawa's Jitte
take note of how there are ZERO 1CC cards in the main.
As for Hangarback Walker in Vintage: It is great with Ravager. Ravager is awesome in Vintage because it gets arounds cards like Dack Fayden and Bridge from Below. Hangarback Walker grows tremendously when the games are taking a long time, and are slowed down because of Sphere effects. Ravager and Hangarback Walker are also exponential, much like Monastery Mentor.
In Legacy, Hangarback/Ravager miss being able to sacrifice excess moxen and dying artifacts, so the only way to make the two of them playable is to also include Steel Overseer. Which simply hasn't been figured out by anyone else who plays Legacy, and that doesn't surprise me, because Legacy players are generally good technical players but terrible (and by terrible I mean unoriginal, awful, lousy, lazy, and pathetic readers of net decks) builders. Proof of that lies in the 0 new creative decks that top 8 Grand Prix Seattle and the 0 innovation that has happened in the format, while Vintage can't get 1 deck from a top 8 to carry over from one major event to another. Hey legacy players, net decking a stock list and changing 5 of the 75 cards is not innovation.
Legacy is dead because the people who play it suck, period.