There could be many reasons and they would depend on the variety that you have. What are they? Macrophyllas? Paniculatas? etc?

I believe macrophyllas they have the round pink blooms and grow on old wood. The only thing I can think of is too much fertilizer. At beginning of spring I spreade composted cow manure mixed with Garden tone around them.

Did you have a Srping freeze or a cold winter?

Periods of insufficient water starting when the plants developed the flower buds (in July-August), plants that are not winter hardy, unusual weather that killed the buds, pruning at the wrong time (but you said you do not prune), pests like bunnies, squirrels and deer... all of these could affect bloomage.

Last year we were in a drought. We did not have a bad winter-maybe I better say it was no different than usual. It can't be bunnies or squirrels due to the flowers that will normally bloom on top r not blooming. There r low hanging blooms. Well this year we r getting lots of rain. Maybe next year will be better.

In zone 6, bigleaf hydrangeas (Hydrangea macrophylla) that bloom on old wood need winter protection in order to ensure blooms. Even "normal" winter weather is cold enough to damage latent flower buds but often the damage comes with late frosts in early spring as the plant is coming out of dormancy.

In zone 6 and below, cold damage is the number one cause of failure to flower after improper pruning.

If you search through the archives of this forum, you will find multiple threads discussing this issue. It is a very common question :-))