How did a small agency charged with collecting the tax on tobacco and booze grow into this? Do they still pay any attention to their “alcohol and tobacco” mission?
They no longr collect the taxes that were their fig leaf for existence. They do still enforce the laws (and make the regulations which the also enforce) on transportation, packaging and so forth. They are now part of the "Justice" department, not the "Treasury" department, where the tax collecting is still done.