Actually there are a couple of things. One the shear magnitude of the effort, and the fact that while. as you say. the FFLs are required to maintiain the records, the feds are prohibited from doing so themselves. They can legally trace individual guns, but "forward" tracing is (supposed to be) illegal. I'm pretty sure that the FFLs are not required to turn over their records anytime the BATF asks for them, but are required to provide information on specific weapons in the course of a criminal investigation. Having the records exist at all is dangerous, but not nearly as dangerous as having them all in a BATF computer in the District of Criminals.
How many FFLs would really dare to refuse a request from the BATF? They know the BATF can put them out of business in a heartbeat.
Having the records exist at all is dangerous, but not nearly as dangerous as having them all in a BATF computer in the District of Criminals
How much has this difference slowed them down in the case at hand?