Because IDPA promoted itself as such. Still on their homepage, they infer that they are:"The International Defensive Pistol Association (IDPA) is the governing body of a shooting sport that simulates self-defense scenarios and real life encounters."
Some IDPA shooters will tout that they are defensively trained...which they are not... and will say that IDPA is NOT a game...which it is...hence the comment you ask about throughout the shooting community.
While any shooting competitor is better off than someone just punching holes in paper once a month, and it will help with your gun handling skills, it is NOT defensive training.
