What would cause my pole bean plants to grow very tall but not grow beans?

Over-application of high nitrogen fertilizers or otherwise high levels of nitrogen in the soil, especially if the extra vegetative growth was especially dark green. The symbiotic bacteria that colonize legume roots fix atmospheric nitrogen into easy to utilize compounds for said roots. Therefore, adding additional high nitrogen fertilizer will result in too much nitrogen for healthy plant development. Symptoms include failure to set fruit, as well as large plant and leaf growth. New leaves are often dark green, and leaves set in greater numbers than is normal.