No traps have a rez cost. It requires you to install it to go off -- something many things don't request. You can't advance it outside Mushin, so there's less ability to bait a cautious runner. Bid 0 on Psi risks the runner doing very much the same thing, and that's generally the right bid to make unless you've got a read on your opponent's position. Psi isn't a guarantee, if they hit you might have whiffed, which isn't a big issue but can be annoying in comparison to, say, Snare.
It's also just a big opportunity cost. It's not a Snare, Shock, or Shi.Kyu -- all of which protect some combination of HQ, R&D, and Archives -- the servers most likely to get hit -- as well as being installable. Advance traps like Junebug provide something to Trick of Light off of. Edge of World and Psychic Field... don't. Makes it a bit harder to find more slots that can be filled with traps as opposed to Ice, economy, and the like.
It cannot kill the Runner. You can, on a follow-up turn if they're out of cards and can't draw more, but hitting Psychic Field isn't going to lose the runner the game inherently... unless you've got a House of Knives scored, I guess (haha, still a part of the run, sucker!).
Not to say that it's bad. There are a number of decks that really like having it -- especially decks running SanSan, to keep it from being trashed so easily. It's a bit swingy, which can be good or bad, and a lot of people don't run unadvanced Jinteki servers anyway.
tl;dr -- it's good, with some drawbacks in comparison to other things -- no kill shot, no ToL if unrun, only works in a server -- that balance it out. It can slow them down, but it's a trap through and through. It doesn't keep your centrals safe, if they don't fall for it it doesn't do anything for you, and it's yet another card eating up Jinteki deckspace to fit the "we have traps" plan, against strong competition.
EDIT: Corrected by @JohnnyCreations, no window to use HoK after they access. So, yeah. That'd be a big part of why.