Cold winter temperatures may kill the flower buds. This often happens to forsythia. Unfortunately, nothing can be done to prevent this type of injury. Plants that are not fully hardy will be most susceptible to cold injury. Improper pruning may cause failure to flower.
Some plants bloom only on last year's wood, particularly spring bloomers like lilacs.
Cutting the plants back severely removes all the flowering wood. This may happen most often on climbing roses. Overfertilizing with nitrogen can sometimes cause plants to grow only leaves and stems. Such plants will be quite large but without flowers. A plant may fail to fruit because of all the reasons I've listed for failure to flower.