Here's why:
The defender is the only role that is specifically built around decieving the monster.
I would disagree. The Defender is not built around deception at all. The Defender is built upon
threatening enemies, not "deceiving" or "surprising" them.
You are spending every action attempting to get all the monsters in the area to attack you. If you are simply unable to do your job because everything you fight understands that, and ignores you at every turn, that is a terrible way to play any game.
Actually, your job isn't to get all the monsters to attack you. Your job is simply to make it much harder / costlier for monsters to hit any of your allies. If that means giving the enemy -2 to hit and dealing an extra OA every round then so be it.
Every decent defender class (so, basically all the defenders but the Paladin) has a satisfactory build that motivates the enemy to pay attention to said defender. Every if it doesn't always convince the most savvy monster to leave the squishier characters alone all the time, it still makes it harder and more expensive to try and drop the Rogue on the other side of the flank dropping 3d8+7 damage per round with an at-will.
There are two huge player errors I see that create big problems playing Defenders.
1.) Trying to make a Striker because Fighters used to be melee damage hounds in previous editions.
2.) Trying to build an impervious tank under the assumption that monsters will be forced into fruitless attacks against you.
The best way to motivate monsters to attack your Defender is a combination of increased penalties for failing to do so and reduced penalties for doing so. Defenders have a ton of healing surges for a reason - they are
supposed to get hit. Even most intelligent monsters will be more motivated to attack a fighter round after round if their attacks are actually dealing damage.
Monsters that can't scratch a tin can with a low threat level
are going to turn around and devour the high DPS guy in leather jabbing them from behind. Defenders should plan accordingly.
- Marty Lund