Because (1) it's a fantastic run hot deck (Cosmo's deck from champs, for example, doesn't have Preordain. It's going to fold on itself some medium percentage of the time, though I'm sure it's fantastic when it does not), and (2) it doesn't have any real champion online who is willing to grind the deck and get the 3 to 4 5-0 records it takes to get noticed. (and a big #3--it relies on your opponent not knowing what you're doing a little bit).
Cheers everyone. I find some of these responses a little odd, in that I'd expect that "true competitors" wouldn't really care about the hybrid playstyle if the deck is good. But then again, Vintage is a weird format and people don't always just want to play what's good, so maybe you're right.
It's the quintessential Mana Crypt deck of the format, relying on multi-powered openers even a tad bit more than Paradoxical Outcome. When its openers are highly powered, it's an awesome deck. But in the +50% of the time where they're not, you end up in ugly situations where you're paying 4 and tapping out to lose a Thief to something that costs your opponent 1. (Bolt, Swords, Pyroblast). If you don't develop your mana base aggressively in the early game, you tend to get run over. And it's not the most impressive card v. Workshops or Dredge. Even a dead on arrival planeswalker is usually preferable there.
I say this as someone who loves Notion Thief and defended it even when a certain personality called it "bad" because "it didn't have flying." I prefer running it with Caverns. Champs didn't seem as totally saturated with 45,000-Pyroblast decks as MTGO and this may have contributed to the success of Thieves.
Hi, the guy who top 8'd EW here on 4x notion thieves + wheel + twister.
A lot of the others already mentioned some of the inherent issues.
@neo_altoid to answer some of your points: 1) I wouldn't say I ran hot to be honest. Both of my losses in the swiss were not due to bad luck, but actually my own misplays, though Sperling's pyromancer deck matchup didn't feel great. Even my loss to in the top8 to PO felt like my opponent had better variance than me. Not having preordain (or ponder) speaks to how I like to play the deck (and my playstyle in general). Less fluff/air, more "real" cards. For the most part, the deck ended up trading resources and coming up ahead because there was less fluff. 2) I don't play on MTGO, but if I did, I would probably champion this deck and grind it all the time. 3) And yes, I did get some people because they didn't play around the 2nd or 3rd or 4th thief.
It is definitely a weird deck, which I would classify as midrange with combo type aspect, which sometimes is difficult figuring out the role in the matchup/situation. Has the tools to do a lot and the combo aspect means it only has to midrange for so long or act as control for so long, and sometimes just starts the game as oops I win.
My feeling on the deck is that it is probably heavily meta dependent. Dredge and shops are probably not the best matchups, but the tinker-bot/vault-key combo aspect of it allows it to steal games from them. It is best when blue without much interaction is running around (aka a lot of Paradoxical, where their only interaction is countermagic and an expensive repeal). The less swords and pyroblasts there are, the better notion thief is; I was lucky to not face pretty much 0 swords, and pyroblasts were plenty but I was able to grind out the pyros with multiple threats.
Also, it is not best at any of the archetypes it hybrids as, which is tough to not just play the best deck of the archetype of the format. I like it because I can play multiple roles with it. That's just my playstyle, maybe not an easy or correct way to approach vintage.