Their economy collapsed 40+ years ago and illegal immigration is the only thing that has prevented a violent revolution from occurring. The PRI is just another corrupt quasi-communist political party that stripped their nation's wealth to line their own pockets. They allowed the election of Fox as President just to keep the rightists from defecting from the ruling class. PRI still controls everything.
Do you think we should invade Mexico, force a regime change, and install a democratic government down there? That might cost less than paying for their welfare and health care benefits up here.
And apparently our leaders have seen to it to support the few communist elites.