Why do some vitamins contain sugar?!

That's the difference between buying natural health products at a reputable health food store and a drug store or supermarket. First, the sugar is a cheap "filler" to bulk out the tablets, and it makes them more palatable to some people.
Sugar is to modern day patent "medicines" what alcohol, cocaine and opium were a hundred years ago in so-called "health tonics".
An example of another gimmeabreak deal is finding high fructose corn syrup added to a really healthy food like Japanese seaweed. Arrgghh!

Because some companies believe that they will "taste better," which means more sales and they are part of the conspiracy, to lace nearly all foods with sugar.