Some possibilities:

1. If not given plenty of direct sunlight during their early vegetative growth period, bougainvillea may not form blooming buds. If these buds are not formed early in the growing season, the plant won't flower later.

2. If the plant is heavily fertilized (gets a lot of nitrogen), vegetative growth may dominate and blooming will be reduced. If your bougainvillea has grown more this year than in previous years, it may be getting too much nitrogen, resulting in fewer/no flowers (colorful bracts).

3. Bougainvillea flower best when they are planted in relatively smaller pots. If you've upsized your plant's pot this year, it may take time for the plant to grow into it's new container. The Goldilocks effect can have a significant impact on flowering.