I rather think the question was why ferment potatoes? But although I have never tried to make potato wine I have a book (no date of publication, but it looks like a late 19th Century publication. early 20th) that contains two different recipes for potato wine... neither of them are very um... convincing... but clearly this was a wine that was made in the rural past - one recipe involves boiling the tubers and using the resulting liquid and the other is more similar to banana wine where the potatoes are not cooked in the liquor but mashed and the resulting mash forms the basis of the wine... But both these wines require additional sugar and raisins and the like...