The issue is that people can change how they own things so they don't have to disclose. The law is necessarily public and people can adjust the way they structure ownership accordingly.
We see this all the time already. For example, Medicaid won't pay for your extremely expensive end of life care if you have assets. So, people give away their assets (to a trust, to family) before applying for Medicaid to cover their nursing home. It becomes a game of cat and mouse. People will adjust where they can to avoid tax.
This also already happens with income tax. For example, executive compensation is primarily provided as capital gains rather than income because it's much more tax efficient. Everything is in the open.
The other issue here is one of cost. The IRS has to fund the cost of analyzing filings and deciding to audit. This is very different from a post-judgement scenario.
