There are several reasons:
The HelB solution is an enterprise solution and for several reasons can not rely on phones carried by bus drivers: phones may be forgotten, or they may malfunction, the movement of the driver would affect the results etc etc. Also the phone would not be able to record the engine temperature etc.
But Ahmet, this is a good question since phones can register velocity, acceleration, position, location etc, which can be used for gathering data on the phone user and used for value creation. Many possibilities!