I always held that 9/11 was dubious. Not an "inside job" per se, but definitely a case of "we're gonna turn our backs for just a second, and you terrorists better not do something silly while we're not looking!"
I don't doubt that many proposals were made well before 9/11, but that attack certainly proved a catalyst in getting them approved.
Basically: we want to control citizens > citizens don't want to be controlled > create a scenario in which they want to be controlled > control citizens
Might take a few years between implementation and the desired result, but politics is always a slow march towards authoritarianism.
Also, the fact it was labelled as the counter terrorism act. Not much call for a counter terrorism act of there isn't much terrorism happening. No better way to say "we need this" than an actual terrorist attack happening.