>>andy_p+Da
Is this a real question? Legally buying guns in the US come with registration of serial numbers, names, and addresses. Printing a gun does not. Printing a gun also does not need to wait for a multi-day delay from a background check. Depending on the printer, it could just take multiple days to print.
Asking why someone would want to do this is just not trying very hard in the conversation is actually pretty myopic.