A number of Congressmen, including my normally useless Representative Jim Banks, wrote a letter to the ATF squawking about it and that probably helped a lot.
Still, this is nice but everything changes in a month when Biden takes office.
They ATF quit on this awfully easily. That makes me suspect the whole thing was a trial run and that once Biden is in office, he will issue an executive order of some sort and armed with that order the ATF will go back and try this same scheme over but for real this time.
Pistol braces are low hanging fruit and will absolutely be on the chopping block, especially if the Democrats repeat their success in stealing the 2020 general election via widespread fraud and taking the Georgia Senate seats. Enjoy the win while you can but don't think for a second this is anything other than a temporary reprieve.