The funnel within the bee trap adds extra light to attract the bees to the trap. See when the bee goes in here, he’ll want to exit immediately because he realizes it’s not a good place to nest. At first he thought it was a good nest, but it’s not. And when he wants to leave, he flies toward the light; the same way a fly goes to a window in your house. But when he flies to the light, he ends up in this little funnel. He may continuously try to get back up and out of the hole, but eventually he will get tired and fall down inside. Once inside, he is trapped.
Note, a wasp may go in the trap and leave, but if a Carpenter Bee gets in there he will never find his way out.