I understand that, but a lot of gamers can figure some games out without a forced tutorial. WASD movement, jump with space, crouch with control, sprint with shift, move camera with mouse, shoot/attack with left click, etc. A lot of designers/developers became so desperate with the possibility that their game might be "someone's first game of that type" that they choose to force everyone to play the tutorial right at the start, even players that finished the game and decided to start again, and leave it at that.
The tutorial as a main menu option fixes both problems.