Government boondoggles like the wall would fill up more than several times the running time of the movie. That's not hard to belive... If you go by the logic of the movie, the Jaeger program was a failure too... Once there were hundreds, only four were left... They were no longer effective as the aliens adapted their monsters. It's likely only a new Jaeger program with improved systems would have worked.
ell, remember; the reason given in the film was that the Kaiju were destroying the Jaegers faster than they could be built. That said; after they had an incident where a Kaiju breached a wall like it was nothing (and was defeated by the one (and only) Jaeger Mk V; you would have thought someone, somewhere would say:
"Hey, maybe we SHOULD start funding the program again? It may be a loosing battle, but it still works better than these walls."
(But again, applying any logic to this film really ruins the fun of stuff like: "Where the hell's my shoe??!!")
[And I'm said to see the film underperforming in the U.S. -- although indications show it opened very strong overseas and should really be a hit in japan as this is the kind of film (with these level of digital effects) they would love to make, but just don't have the budget resources as spending that much locally would net zero profit for them.]