Are they getting more shade from trees nearby growing taller? Do you, or your neighbor, fertilize your lawns(s)? Most lawn fertilizer is high in Nitrogen, and will push leaves instead of flowers. Aside from those two probable causes, I can't think of another right now.

You can TRY to fertilize with a fertilizer for flowering plants, with a low N (first) number, but if they are getting too much shade, there's not a whole lot that will do to help.

While CMs do OK with little or no water, especially older ones, they do better with water, so maybe getting supplemental water to them might help. Of course, if you are under water restrictions, that's no use....

They are getting full sun all day. I do not fertilize my lawn. . . have a lawn sprinkler system and my property is located at the junction of two creeks so water is not a problem. . . also it has been a very wet season here. My red CM is flowering fairly well now; however, the white and pink CMs are showing only a few blooms. Maybe fertilizer is the answer. I read where blooms grow on new wood. . . maybe a mild pruning is the answer?

Just dropped in from S. Florida, and mine are just starting to bloom well here. DON'T PRUNE! At least not until they bloom. When I lived in SC, sometimes mine skipped a year of blooming (I had along row of 18 watermelon reds up my driveway), but when they did, they were gorgeous! Also, it seems the whites bloom later than the others.