Marketing. Now people beer=bad, dog beer=good. There's probably a "crises" caused by the "epidemic" of insensitive owners allowing their dogs to drink their beer.
Personally, I PREFER to pour some in the cup of my hand and let him lap it out to having him accidentally on purpose knock a full one over so he can lap it up off the floor.
I jest pour it in her dish and let her satisfy herself at her leisure.