Because, most of the time, the grand jury no-billed the indictments.
As to the topic at hand, were your examples of prosecutions in a post-September 11th world?
No, they weren't. But there were a lot of "illegal alien crime wave" stories in the press at that time.
As every survey has indicated that a minimum of 2/3 of the country opposes illegal immigration, I doubt your premise that the public does not support these laws.
People oppose illegal immigration in the abstract. When concrete proposals for effective enforcement are proposed, they oppose those proposals more than they oppose illegal immigration, because those proposals will, if enacted, personally inconvenience them more than illegal immigration does.
Bottom line: a guest worker program will make it far more convenient to hire legal employees than illegal employees. This will greatly reduce the incentive to hire illegal aliens, which will reduce the incentive for illegal immigration, and thus reduce illegal immigration attempts; reducing illegal immigration attempts will, in turn, make it easier to detect, identify, and apprehend illegal immigrants.
But, instead of fixing the underlying problem (a broken US policy that has been demonstrated to be unenforceable), you insist on trying to keep a bad policy in place against the wishes of the American people (as expressed by their behavior).