It's high risk/high reward, vs low risk/low reward for lower income households. However I'm sure there are things like qoutas, etc. that push auditors to go after the easy wins.
Not to mention you loose some big cases against wealthy people cause they have a lot of money, and they come after your job or make the IRS look ineffective.
Haha given Kevin Sorbos went down a similar path, this is pretty fitting.