This rule came about without any change to the law, the ATF just decided to change their minds and reverse previous findings and suddenly render millions of guns illegal. This is strong evidence that we live in a post constitutional nation.
It is also why it will eventually be completely killed. In the meantime the compliance date has passed, so if some people complied will they be reimbursed for the cost?
https://www.ammoland.com/2023/11/federal-judge-stays-entire-atf-pistol-brace-rule/#axzz8Iabhh082