Question

why do you think rolling friction is less than sliding friction

Answer 1

Rolling friction is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. Sliding friction is the force resisting the motion when a body slides on a surface. The force of friction depends on the area of contact between the two surfaces. As the area of contact is less in the case of rolling than in the case of sliding, rolling friction is less than the sliding friction. 

Answer 2

Rolling friction is the resistance to motion experienced by a body when it rolls upon another. It is much less than sliding friction for same pair of bodies. When one body rolls upon another, there is theoretically no sliding or slip between them. And if both are perfectly rigid, there is no surface of contact.