There are multiple reasons for dogs to get excited after a bath. It could simply be instinct! Most dog shampoos have perfumes that may smell pleasant to us but smell awful to animals. They try to roll around and rub the scent off of their coat as quickly as possible. Their excitement is just an effort to mask the unpleasant and un-dog-like odor.
The excitement of your dog running and rolling around may also serve as a way of transferring water from their fur to your carpet, furniture, and bedding. Or, your dog may feel invigorated from the stimulating massage during the bath due to its relaxing nature. It’s natural behavior.