In fairness, I can see both sides of the coin with this one. When we think about this more... "realistically," some people prefer baths, as it can offer more comfort and enjoyment... especially when soaking with bubble baths, essential oils/herbs, or mud. while others prefer a quick wash in a shower... especially with a showerhead that can produce a "rainfall" type of effect, which to some can be found soothing and release sore muscle tension. To each their own.
Yet, I agree.. they should each be be preferred on the basis of a Sim's personality trait, mood, or other preferences... not be designed to just automatically go for the tub each time.