physical chemistry - Why are there distortions in electron cloud in molecules? How does increase surface area amplify these distortions?

In the physical properties of hydrocarbons,it is said that branched hydrocarbons have relatively less boiling point than it's linear form. From what I have learnt is that it is due to the increase in the surface area of the molecule which increases the intermolecular force. Now, this intermolecular force is the london dispersion force which happens because of the instantaneous distortions in electron cloud. This means the more the surface area of contact the more the ease of these distortions in electron clouds. This explains the strength of intermolecular force of branched and linear form of hydrocarbons and thus the difference in boiling point. But why there are distortions in the electron clouds? Why surface area has to do with these distortions?