Or the real reason - Lucas done fucked up.
And the explanation is bullshit - why would you have to maneuver around object while in hyper space? Those objects don't exist in hyperspace. And we see them make the jump several times in the movies, and see no maneuvering. The concern with hyperspace, warp speed, etc. is always where you are when you come out.
If you want a real (fake) explanation, you'll have to go with the simple fact the Han is a smuggler. He's evading imperial ships, systems, outposts, etc. He has shipments to make. Optimizing the Kessel run for distance instead of for time can be anywhere from a pure traveling salesman problem to a sneaking problem.
But this doesn't help either - the speed and maneuverability of a ship has almost no bearing on how detectable it would be to fixed scanner installations, nor does it have any bearing on how much distance would be required to travel a planned route.
Lucas fucked up.