It helped me get back one of the firearms that was stolen from me.
I had a pistol that was recalled for a safety issue. The recall was for pistols in a specific serial number range.
So serial numbers have other legitimate uses.
Just because it can be occasionally helpful does not make the requirement to have them constitutional. Serial numbers can also be useful when attempting to identify when a particular firearm was manufactured. If the SN requirement goes away, gun manufacturers may change to some date-based system for historical information like that.