What do you think accounts for the diffidence between the starting friction and the sliding friction

Once inertia is overcome and the object is in constant motion then sliding friction will mostly depend on the surface, environmental factors (wind, ice, etc ...).

example:

To push a piano from 0 to 1m/minute you would need to over come a huge force pulling down the piano (gravity) but if it were already moving ... to push it, it would require less force, if the environment (and the surface) was smooth and not uphill.