Cos it costs money. Money the federal government doesn't have and wouldn't spend if it did.
It's the same reason they didn't regain control of the screening points the day after 9/11 by making all screening staff public servants with proper training, pay and conditions so decent people would want to work there. They were full of empty promises about how it would all change, but in the end nothing did except for the ban on tweezers and knitting needles.
Instead, despite all the whimpering in the press about how they're 'committed to aviation safety' the Department of Infrastructure is happy to leave the basic security checks up to a bunch of poorly paid and minimally trained subcontractors, employed by companies who won those contracts through the tender process by undercutting all their competitors and cutting every corner they possibly could. These are the same badly trained private subcontractors that the DOI would be happy to see frisk search 'random' people, despite the fact that until now, frisk and strip searching powers have been strictly limited to government employed law enforcement officers (who are required to have a level of security clearance, background checks and basic intelligence) with recorded and challengeable reasonable grounds to do so. The only exception is privately run prisons, so basically aviation workers get to be treated the same as convicted criminals
.
Don't assume that the government wants effective security (as the Israeli government provides) because it's a flawed assumption. What they want is the impression of effective security at no cost or responsibility to themselves.