Q.Why don’t my bougainvilleas bloom?
I live in South Florida. They get plenty of sun and water just from the rain mostly.
They look hardy and have lots of leaves and branches.

Certified GKH Gardening Expert
Usually, when a plant has many healthy leaves, and are very dark green then this can indicate that there is too much nitrogen in the soil. This will prevent blooming. You will need to balance this out with fertilizers high in phosphorus and potassium, and little to no nitrogen.
This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/vines/bougainvillea/bougainvillea-garden-care.htm