I read a book about the IRS once, the author used to work there. He said that at one time there was an extremely high correlation between a certain type of trust and tax evasion. It wasn't a trust that many people had, mostly all rich people using it to avoid paying taxes.

At the time, it was still mostly or all paper returns. They ran the returns through a scanning program that extracted key info for their database and then filed the actual paper return in a box somewhere. He proposed altering the scanning program to record when someone put this type of trust on their taxes, and then manually reviewing them to see if it was legitimate or tax evasion. He estimated they would recover millions, but the software department said it would be around $10,000 in programming costs, so his bosses shut it down.

The book also said that they don't go after rich people because they'll hire a team of lawyers and fight for years, so the IRS mostly targets poor and middle income people who can't afford to fight them and they can just slam them with penalties and fees or negotiate a settlement where the taxpayer waives their right to contest it in court.

It's basically the IRS's version of when a prosecutor charges someone with a dozen crimes to get them to make a plea bargain and plead guilty to the charge they really wanted to convict them of in the first place so they get the win without having to go to trial.