Feet definitely can be extremely hot, whether they are clean and soft or not necessarily. Lovely pantyhose or stockings sensually covering them, while still leaving them perfectly visible just add to the appeal, so does a pair of cute high heels, and elegant pedicure.
They can not only be used for giving direct pleasure, but also for teasing and provoking the other person. There's a lot more that can be done with feet aside from a simple footjob.