It is possible your tulip tree has the best quality of food available to the pollinators.
I don't know about the other pollinators but honey bees seem to visit some plants one season and ignore them the next Lavender, sunflowers redbud, dandelion and crocus. Those plants are visited every year by our bees. There are others they visit every season but those come to mind off the top of my head.
Honey bees will travel a three mile radius from there hive to forage. They select the best quality they can find.
