I think of all the various talents a cyclist may have, sprinting is the one that is most looked down upon. In the modern era in particular where lead out trains are concerned, it makes sprinting seem even more easy. Maybe because a lot of us have raced and we hated that guy who would sit on, do little or no work and then re-appear to take the victory. A little bit of envy perhaps.
I also think people see cycling as a sport where hard work and commitment are rewarded and I guess people just feel that someone hiding in the peloton until the final 200m is just not very worthy of admiration. Whether you are a climber, a TT, a rouleur, a cobbles specialist or even a puncheur, you usually have to put your irons in the fire a lot earlier than the final 200 so there is more of an obvious respect for having "earned" a victory.
There is also an obvious difference between sprinters like Maertens, Kelly, Vanderarden, Freire, Ludwig, Zabel who could also contest "tough" classics and the more pure sprinters like Van Poppel, Abdu, Cipo and Cavendish. I respect pure sprinters for what they are but like most people, I view them as the lowest "breed" of talent in the cycling hierachy chain and the idea of them being World Champion makes me cringe.