Could be several issues. Placement, scent, and individual preference all contribute to whether or not a cat likes a particular bed.

If you haven't already maybe try putting a worn tshirt on top of it so that it smells like you and put the bed in a place he normally likes to sit. If he still ignores it then there might just be something about that style or size of bed he doesn't like.

If he responds to catnip then sprinkling it on the bed might also get him to warm up to it.