Why is kinetic friction present when two objects are slipping across each other

When you send a bowling ball down the alley, it starts by sliding. The kinetic friction force (predicted by the coefficient of kinetic friction) on the bottom of the ball produces a torque which causes an angular acceleration. When the backward tangential velocity of the bottom of the ball (measured relative to the center of mass), matches the forward velocity of the center of mass (measured relative to the alley), the ball is rolling, and the bottom is in static contact with the alley. There may be a small “rolling friction” due to the deformation of the two surfaces. If the ball then rolls up an incline, there can be a static friction force acting up the incline (which matches the loss of angular velocity to the loss of linear velocity). The static force has an upper limit predicted by the coefficient of static friction. Static and kinetic friction originate at the microscopic level where the peaks and valleys of the two surfaces inter-mesh. Generally, kinetic friction is a little smaller than the maximum allowed static friction (the moving surfaces are bouncing peaks off of peaks).