Because they may be content with drawing as black and seek an (ever so slightly) easier win as white. It depends on many factors: relative player strength, dura

Because they may be content with drawing as black and seek an (ever so slightly) easier win as white. It depends on many factors: relative player strength, duration of the match, how players are paired in tournament rounds, current standings in the tournament, and so on. A computer won't do this kind of reasoning.