Check the depth of their roots. If their roots (or tubers) are deeper than 4 to 6 inches from the surface you should dig CAREFULLY around the entire plant to see how deep it has been planted. Gently lift the peony plant up, but not totally out of the hole. If it's too deep, put some of the soil into the hole under the plant. Keep filling in the soil until you've raised it all round; pack the soil gently, then water thoroughly. When you're finished, the eyes on the roots shouldn't be more than about 1-1/2 to 2 inches from the surface. Peonies are really fussy about how deep they are planted in order to bloom!

The other possible main cause is lack of sun. You don't say exactly where they are sun-wise, but even if you were in southern CA (or even FL), you must give them a very sunny position. 6 to 8 hours a day of direct sun in spring and summer is optimum. Mine are quite happy in USDA zone 8 equivalent but are in a directly south facing position. Hope this helps. If it doesn't, come back with more details as to watering habits and soil type etc.

The height of the foliage sounds suspicious, even the one in our garden which does not flower has stems of up to 3 feet tall.