Gee, one requires huge industrial laboratories complete with niche equipment, highly-controlled precursors in massive quantities, and trained chemists.. the other requires commonly-available machinery and universally-obtainable, cheap materials and a scrappy high-school student who excelled in shop class.

Seriously, you have no idea what you are talking about. I can have a receiver milled from billet in the time we've spent discussing this.

Even the data you linked explains:

Privately Made Firearms Law enforcement agencies recovered and submitted 37,980 suspected privately made firearms4 (PMFs) to ATF for tracing between 2017 and 2021. It is probable that current trace data significantly underrepresents the number of PMFs recovered in crimes by LEAs due to a variety of challenges presented by PMFs, to include: • PMFs involvement in crime is an emerging issue and LEAs are just beginning to institute uniform training on the recognition, identification, and reporting of PMFs that can lead to more accurate PMF data being collected. • PMFs by their nature may have no markings at all, duplicative markings, counterfeit markings, or markings that appear to be serial numbers on parts of the firearm other than the frame or receiver. These duplicative, counterfeit, or erroneous markings can be mistaken for authentic serial numbers and markings causing law enforcement to not recognize the firearm as a PMF and/or potentially follow false leads based on these markings. As Figure OFT-04 reflects, the number of suspected PMFs recovered by law enforcement agencies and submitted to ATF for tracing increased by 1,083% from 2017 (1,629) to 2021 (19,273).

So, just domestically, home private firearms manufacturing totaled more units than all guns traced into Mexico in every given year.