In addition to the reasons you and BobAjobb gave for moving the brake away from the rim, are two more:

• Damage to the rim such as a bad buckle doesn't prevent use of the brakes
• No need for a brake track on the rim which provides potential aesthetic, aerodynamic, and structural/material benefits

Like you, I'm not saying you have to move to rim brakes (I haven't and it won't influence me until I want/need a new bike anyway), but these are the rationale for disc brakes, so suggesting we should just switch to hydraulic rim brakes and call it a day, misses the point.