Looks like cercospora leaf spot, a pretty common fungal problem with a number of different types of hydrangeas.

And we need more info, please. Where are you located? Do you know what kind of hydrangeas you have? Aside from any rain, how do they get watered? How much sun and when?

We are in middle TN. We are on well water so we aren’t generous with watering to avoid running our well down. They probably get a small drink weekly at best. They get full sun from 11-2. I thought I could lay my hands on the papers with the names but no luck. We have had them a decade. Thank you for your reply.

I'm going to assmue that they are bigleaf hydrangeas, H. macrophylla. Flowering on these can be adversely impacted by winter cold and/or spring frosts. They are thirsty plants (hydrangea is Greek for "water vessel") and a 'small weekly drink' is not enough. They don't mind sun in the morning but prefer afternoon shade. Sun from 11-2 is too strong for them.

Being stressed from not enough water and too much sun can cause secondary issues, like fungal problems.

Are these conditions an explanation for no blooms?
Should I prune aggressively in fall and should I water more throughout winter?

If, as it appears, it's a macrophylla you do not want to prune it aggressively in fall. These do not need much pruning. Normally you would leave the dried flowers over winter and just cut the old flowering stems back to a pair of strong buds in spring. Once the shrubs are a reasonable size you can prune out a few old stems to the base to rejuvenate the plant. Possibly they're just not suitable for your climate if you can't water them copiously and have very high temperatures.

Are these conditions an explanation for no blooms?

No. As floral alluded to, macrophyllas are sensitive to cold temperatures and that is location dependent. They are also sensitive to excessive or unnecessary pruning.

The questions regarding watering practices and siting were to determine how stressful the sitation might be that could encourage the fungal issues.