My hibiscus plants are healthy and full of buds but they don't bloom because the buds snap off. I have not seen anything eating the plants. What would cause this?

What could cause this?
It might be too dry... You might have aphids or white flies, or possibly some kind of weevil.

what we need to know is specifically what kind of hibiscus are you trying to grow? Is it In a pot or in the garden? Where is your garden?

Pictures of the plant go a long way toward getting helpful answers.

By the way, welcome to the forum!