how....it's a simple bill attached to your estate
Just off the top of my head:
1. This would kill small business growth, especially if they had tried to expand during some of your taxable years.
2. Business A was bought out by Business B. Who pays for Business A's retro'd taxes?
3. Large companies (that employee tens of thousands of employees) often are buying and selling, going back through 20 years of records would end up costing more than the taxes themselves.
And that's just the easy stuff.
Anytime you open a taxation door for government, it's going to bull as much of its bulk through it as possible (when sold to Congress at the time, income taxes were never intended to get over something like 7%, iirc). Retro'ing any tax would lead to more taxes being retro'd.