These statistics are probably very misleading.
Many of us trade firearms back and forth among acquaintances and even friends. If you personally know each other, the firearm transfer did indeed involve a "background check." The value of personal knowledge was at least one time recognized by the state. For example, it used to be (maybe still is) that a Notary Public could notarize without ID if they personally knew the individual.
Indeed, personal knowledge is actually MORE invasive than a government background check, which can only find things that have been officially reported to the government.
I have a friend that works for the FBI. REGARDLESS of the background check, to be hired they will find many of your relatives and friends and ask them about you. They will do so every couple years while you work there, including talking to ex-wives.