Even running backs and wide receivers have advantages that the quarterback does not. They usually can spot the enemy in time to get down or avoid the hit. Plus, they are moving. Quarterbacks are not. They are stationary targets.
Hits come from the blind side as much as from the front side.
They come from every direction, at times when they are off-balance, just having released a pass, with defensive players bearing down on them. This must change. Roughing the passer rules, with different interpretations in every game, are not enough. The rule should be made iron-clad, perfectly clear, with no subjectivity whatsoever. Any player who touches a quarterback after he releases the ball is penalized.