The trouble is that writing a proof in a format amenable to this verification is harder and much more tedious than writing it for a paper
Here I just want to encourage anyone who thinks he's a good programmer to develop such a system. It would be extremely useful for education as well: students would get a tool that explains complex proofs, and professors would give assignments to put a theorem into the system (if student is able to enter the theorem into the system, then he/she definitely understands it up to the very foundations). The main problem to solve is good UX, not the math.
They who manage to make the system, the new verified Wikipedia for Math, would have their names inscribed for eternity, because Math is eternal.
Also, this is a lot harder than you think. "Extrapolating" from a learning set is relatively easy to do for statistical problems and prediction, but proofs are hard.
Shouldn't you be able to build a database of all current proofs and have a computer be able to cross-reference and extrapolate from that? Sure it would be far from trivial but it seems doable. Mathematica/Wolfram for instance should be half way there.
Here's the golden chance for a programmer to win x amount of Nobel prizes! :)