Most people don't consider alcohol and tobacco drugs, also alcohol, tobacco and guns have been around in the US for hundreds of years. Pretty much all the drugs that the DEA covers are relatively new compared to alcohol and tobacco, Cannabis is probably the only exception but even that wasn't nearly as common to grow and consume as the other two. The ATF was founded a year before the DEA.
Me either, I looked it up to figure it out and was surprised as well. I thought they were founded further apart. I think the ATF had a different name formerly.