1. the IRS has to justify why they aren't investigating the 10,000 known fraudulent not-for-profits, lobbyists, churches donating to terrorists, mayor with $20,000 salaries buying a yacht after 1 year in office, Congressmen with the wives, children, and dogs on the payroll, etc. "No, really, we were very busy - and these guys are EVIL!"
2. they don't need to sue - they have their own Court, and they write the rules. If they lose (how could that happen?) they appeal (meaning: ignore their own Court and drag their feet), if they win they seize anything you own - or that they say you own.