Question for all about expired visas

ALL of the 9/11 hijackers had expired visas and traveled freely in and out of our country prior to the attacks. Once this fact became known, why didn't we(our government)clean house and throw out EVERYONE who is living in this country illegally, like the 9/11 hijackers were?

Yea wheres that "clean everybody thats not a US citizen button again?"

If only it were as simple as you're saying