No reason at all ...
On the other hand, i see no realtion between Warrior and his pull ... Warlock and his teleport on other party members ... Wizard and his reflection of any projectiles ... Ranger and his charge ... Rogue and his darkness ... or Cleric and his livesaving ... either.
I mean yeah, Rogues usualy do want to hide ... but they rarely want to blind themselves as far as i know.
And also yeah, Cleric fits quite well ... as long as you play Life Cleric ... play Trickery or Death domain and the relation is gone. :-/
So far only later added classes looks like their tadpole power is actualy linked to their class ...
Druid > a form ... Bard > a song ... Barbarian > a damage to enemy and themselves ... Sorcerer > dunno, some kind of spell that refresh Sorcery points?
I still dont understand why cant we change Race for our hirelings.

Lets us play Githyanki as racist as they trully are!