1. Artificial flowers may be made of materials such as paper or cloth, which will be deformed or dissolved in water, thus causing the artificial flowers to melt.
2. Petals and other parts of artificial flowers may be made of materials such as plastic or foam, which will deform or dissolve when they meet water, thus causing artificial flowers to melt.
Artificial flowers may be made of chemical materials, which will react with water to produce toxic substances, which are harmful to human body.
These are the reasons why artificial flowers are soluble in water, for reference only.