Also: Why Don't Clerics and Paladins Do More Damage to Undead, Devils, and Demons Than Other Classes?
Maybe all our Clerics and Paladins are not faithful enough.
EDIT: This is an example of how Turn Undead works for those of you who are not aware.
"Channel Divinity: Attempts to drive away nearby undead or force them to cower.
To turn undead you must make a turning check (roll 1 twenty-sided die + your total Charisma modifier) to determine the Hit Dice of the most powerful undead you can effect. Then you roll 2 six-sided dice + your Cleric level + your Charisma modifier to determine the total Hit Dice of creatures in the area that can turn.
Turned undead cower in place or flee. If you have twice as many levels as the undead have Hit Dice, you destroy any that you would normally turn. All Channel Divinity abilities use the same pool of uses per rest.
Turn Undead Mechanics
Turning undead consists of the following checks:
Turning check: A charisma check (1d20 + your charisma modifier) determines the hit dice of the most powerful enemy you can affect (See table below.)
Turning damage: Total number of hit dice you can affect is 2d6 + effective cleric level + charisma modifier (Paladins get a -3 to level.)
Destroying undead: If you have twice or more as many effective cleric levels (Turning value) as the undead have hit dice, you destroy any that you would normally turn. The Mighty Turning enhancement allows you to destroy any undead that has less or equal hit dice to the turning check result."
- from http://ddowiki.com/page/Turn_Undead
I'm not sure if that is 5th edition though.