Well, you are confused and uneducated on the subject, which is exactly why all the convoluted rules and BS exists in the first place. To confuse you. It's most likely true that the feds are covertly ignoring the part of the LAW which states that the recorded transaction/background check for a form 4473 must be destroyed after 88 days and is NOT allowed to be digitized for purposes of data retention ( government database of firearm owners), but why would you just assume they are breaking the law and say "F it", what difference does it make and give them even more information, information that does NOT come with a caveat in the law stating they are not allowed to collect that information for a database?
Here are the facts. A copy of the 4473 which states the serial number and type of weapon is NOT transferred to the government during your NICS check when you buy a gun from an FFL. They are not allowed to have that form or collect them for a database. The only information they have is the type and number of weapons. To obtain the information on a 4473 they must physically go to the place of purchase and look at the paper form 4473. It is illegal for them to digitize and retain that. And even the record of the transaction ( this is the info they were given when your LGS called in to the NICS for your background check) is by law required to be destroyed before 88 days have passed.
We can argue whether or not the feds can already look at your CC purchases or coerce retailers to give them information about your purchases, but that isn't the point. To do that they would have to expend a lot of resources, man hours, etc. Why the hell would anyone be ok just handing them that information already complete and usable on a silver platter?