What makes your hair look bad after using shampoo without conditioner?
It's the water, not the shampoo.
To understand why, you need to know that hair has scales, like a snake. The scales lay flat in an acidic environment, making hair look shiny and healthy--which is why some recommend applying lemon juice to the hair. And the hair scales stand up in an alkali or base environment, making the hair look dry and dull.
What determines the acid/base environment . Public tap water has become "harder," more base, over the years. That causes your hair to be frizzy after washing your hair.
However, shampoo removes the natural oils from the hair, and this removal is what damages the hair by making it less supple and much more brittle. So you replace the natural oils with the oils in conditioners. It helps.