After buying flowers, you forgot to cut an inch off the stems before placing them in the bouquet. The lower part of the stems is usually a bit dry, so they don’t absorb enough water.
The water in the vase is dirty. If the water in which the bloom occurs is old, bacteria can grow very quickly. These bacteria attack the stems, making the flowers less drinkable and drying up faster.
Some stems, flowers, or leaves are dehydrated. As a result, flowers can hardly absorb more water, and dry flowers and leaves release gases that cause more wilting.