Most Helpful Guy
Simply that it's cheaper/lower-end wine. It may lack some of the more complex flavors that more expensive wines have and that some people "require".
It's kind of like drinking KoolAid instead of soda - soda has a bit more of a refined flavor and texture (due to the carbonation), but that doesn't mean that KoolAid can't be a tasty, refreshing drink.
Most Helpful Girl
It's just a stereotype. A lot of wines that come in boxes also have bottled products, but they're all cheap. That's okay though because if you like a wine, freaking drink it. Only asshole wine snobs will judge you for it. I get boxes because it's cheaper and less wasteful.