Time vault is a dead draw without Voltaic Key, and Key is a dead draw without Vault the majority of the time. Sure, there are cute things you can do with Key and Sensei's Divining Top or Sol Ring, but those all take two cards.
Monastery Mentor and Young Pyromancer are combo pieces too. They combine with one third to one half of the average Vintage deck to create an army of creatures. Casting an Ancestral Recall with a Mentor/PMancer out turns that card into a true +3 card advantage, and cantrips like preordain suddenly create a point of advantage too (due to the 1/1 token approximating the value of one magic card). These cards ask so little of you and offer so very much in return, and they have few true disadvantages.
Gush, which goes hand in hand with said creatures, is simply the best and most efficient unrestricted card-drawing spell in Vintage. Much like the token generating creatures, Gush doesn't ask much of you at all, it really just wants you to play fewer lands (and who doesn't want more spells and less lands!).
Since those creatures combo with so much of your deck (instants and sorceries, and non-creature spells). you don't have to fill your deck with janky cards like Time Vault, Fastbond, or hell even Yawgmoth's Will or tutors (although those are probably still good). You get to pack your deck with card drawing and counterspells, which means that you're putting together a winning board state with very little effort, instead of trying to assemble some combo AND find cards to protect it.
The only drawback that the non-broken creature based Gush decks have is that their cards aren't quite as busted and "oops I win" as cards like Oath of Druids or Tinker. The plus side really, REALLY seems to outweigh the downside, as the consistency of a Gush deck seems to be more relevant than the occasional lucky vintage turn one kill.