Sementics of art (watercolour)

Time is not an element of art yet artists are so concern with experience in the past, present and possible future. Some exploit the colour element with rhythm, movement or repeated pattern. Others would create lines and modulated strokes to simulate the flight of time. In anyway, they turn out to be abstracts.
My concern is, why are artists giving up the subject itself, like a clock that shows time, like the moving shadow casted by the strong sunlight. That still-life could be a better 'sementics' of art.