It means that any company can take that code, modify it (as would be required every year per IRS tax changes), and resell it without being required to publish the source code changes.

What many European countries are doing is requiring the government to publish code under a copyleft license. That would allow companies to also benefit from this code to make their own tools (which they could also sell), and it would require them to publish the source code of their improvements.

Basically copyleft legally ensures collaboration. Public domain does not.

That was before copyleft was a thing. Many European governments are now requiring tax funded software to be copyleft.

There are exceptions to that law, such as the USPS. Sounds like we need to contact our legislators to get the law updated

Licensing CC0 is just subsidizing corporations at the expense of tax payers. It should be copyleft because it was funded publicly