They do not feel like they should take up an exotic slot; and their jobs can easily be done by many other things in the game.
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I think having them synergize with exotic armor and subclasses would be a sufficient buff. For example, if you are on Well of Radiance, the healing turrets can activate benevolent dawn. If you have Boots of the Assembler the turret fires faster/ tracks better, but if you have the Stag the turrets add like 10% DR