I am wondering what is the reason a player is not allowed to damage their racquet on purpose, assuming they have another to play with.
Racquet abuse is not the only offense that can lead to a point penalty in tennis. Kicking a bottle, throwing a bag, or using profanity will often lead to a warning from the chair umpire, if not a point penalty (depending on the number of offenses committed that match). These rules are in place to uphold the integrity and professionalism of the game and to ensure that players follow a certain code of conduct. They are analogous to technical fouls in basketball for yelling at a referee or throwing the ball.
To an extent, they also serve to protect offender’s opponent, onlookers, and any officials. Smashing or throwing a racquet can create a safety hazard for those in the area. In addition, tirades can quickly escalate.