One reason may just be the confusion about Michigan's ridiculous smoking ban. The exceptions to the smoking ban are "cigar bars" (which are establishments that have a liquor license and may also serve food, but who make 10% or more of their income from retail sales of cigars) and tobacco specialty stores. The exemption for cigar bars states that no other tobacco products other than cigars may be smoked in cigar bars. I think the intent was to exclude cigarettes to avoid giving cigar bars an advantage over regular bars, where smoking is banned outright, but the drafters just never gave much thought to pipes. Tobacco specialty stores can allow any kind of smoking, and it's up to the specific store to determine what is or is not allowed. I've been to one B&M that did not allow pipe smoking, but they only sold cigars. If a place sold pipes and pipe tobacco, seems pretty stupid not to allow pipe smoking on the premises.
The other exemption is for casinos. Apparently the righteous don't mind banning smoking, but only for those that lack deep pockets for effective lobbying.