All liquids, such as water, oil, and brine, have the ability to shrink their surfaces to the smallest possible size. For example, if you drop a drop of water on a dry table, the water will not spread out flat, but will collect in a circle. This is because the water is trying to shrink its surface as small as possible. This force is called surface tension.
The strength of this surface tension force varies slightly depending on the type of liquid. For water and soapy water, water is by far the stronger. Soapy water has a weaker surface tension and spreads more easily. So when soapy water is dropped on the surface of water, it spreads out as if pulled by the surrounding water.
Thus, the surface force to reduce the size of the surface is weak, which makes it easy to form bubbles, and these bubbles are also easy to break up.