Kitchen cleaners(including and especially oven cleaners) are of the type of solvent to address animal fat based grease. Bathroom cleaners are made for soap scum. In my experience interchanging them shows how poorly they work on each others' quarries. If I were to guess, I'd guess oven cleaner won't work on the bathtub or tile. Just guessing. If the water is harder than usual, the soap scum will be harder to dissolve with a bathroom cleaner. As mentioned, CLR works on hard water and related deposits. A water softener (if needed according to the water's hardness) reduces this and makes it easier to clean the bathroom.