If you can brush your teeth only once a day, when should you do it? Most people brush only once a day and they do it in the morning. But actually, if the goal is to be maximally clean most of the time, the best time to brush would be at night just after your last meal. Same for bathing. Technically the best time to bath would be just after you are the dirtiest, i.e. just after you reach home in the evening.
Then, why do we bath and brush in the morning? Because we bath and brush for “them” not for us. Sure, the goal of these activities is “to be clean”, but the goal of doing these first thing in the morning is “to be perceived clean by others”.
What other things do we do to be perceived as X, rather than to be X?