Because most of the witnesses were interviewed long after the "3 shots" narrative was firmly established and media saturated.
John. If the shots all originated from the same place, and the same rifle, then all shots would have sounded pretty much alike..... A large percentage of the ear witnesses said that the first shot sounded different than the following shots......That first Boom was probably the signal to the shooters to open fire.....And I believe it was a firecracker. I also believe that one of the shooters was using a silencer equipped weapon.