Well it could be for a number of reasons. Both of the plants you mention need full sun to bloom well. If, over the decades, these plants are now in shade due to overhanging trees, their bloom will be less often and dependable. Also, depending on how old your plants are, they may need dividing. Daylilies, in particular, need to be dug and divided every four or five years to keep them vigorous. Peonies can go longer without dividing, but still require it every 8 to 10 years. Both of these perennials are best dug and divided in the fall. Late September to mid October is good.