I have a bougainvillea plant that was purchased (10 gallon) in a nursery in March. It was fully blooming and lush in the container. It was transplanted to the ground this year in spring. So far, it has not bloomed significantly. It receives a good amount of sunlight daily. It is very green and looks healthy and is growing well...just no flowers! I have not detected any pests (caterpillars, etc.) on the leaves or stems. I have been feeding it with a Miracle Grow liquid product. It has been receiving plenty of water due to the large amount of rain we are receiving in the Orlando area. I am not are what else this plant needs so it will have the profuse flowering it once had.
If they are getting enough light (which is the most common reasons for plants failing to flower), then it is likely a lack of phosphorus. Plants need phosphorus to flower. Bone meal is a good source of phosphorus (https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/bone-meal-fertilizer.htm).