> Megacorps have entire teams of people looking for ways to reduce their taxes, many of which are legally dubious but the risk of being caught * the size of the fine means it makes business sense to do it regardless of legality.

"Legally dubious" is the problem, because ambiguous laws are supposed to be interpreted most favorably to the defendant rather than the government, and then all parties have to incur much higher costs because the ambiguity means it goes to litigation, and there is a significant chance that all of those resources are consumed and it comes out in favor of the corporation in the end. The IRS much prefers to find cases where the taxpayer is clearly violating the law.

No, that's a contradiction of your parent comment. In your model, doing more audits would increase "the risk of being caught" and have good ROI.