Because it's a very crude and poorly made cash grab of a sequel, that's why.
You've seen Guy Standeven in something because the man was in everything.

I second thisim convinced there was Gleason- Bandit footage shotone look at the Bandit stunt double, esp when the Bandit first captures the fish looks like the double should be for Gleason- not Reed

It got this rep because of the cut and paste editing of scenes that were shot with Gleason as "Bandit" and then going back and redoing them w/ Jerry Reed and trying to make it fit in with what was already shot. I think once Universal saw the final cut they knew that it would do what they hoped and just put it out for a few weeks. I know in my town it got a decent first week ad in the paper but that was it.

It has a worse reputation than Part II largely because 1) Part III looks extremely low budget, 2) Part III's editing is for crap, and most importantly 3) no Burt in Part III (and to a lesser extent, no Sally Fields).
Other than that, though, no one will ever convince me that Part II is better than Part III. Part III is WAY funnier, does a better job of letting Jackie Gleason do his thing and has a better plot (I know the word "plot" is used loosely when speaking of these films, but let's just say that was better to go with a fish than an elephant for a central theme). There's more action and car-chasing in Part III than in Part II, which gets too bogged down with the Bandit struggling with a clear-conscience over the humanity of an elephant. Smokey and the Bandit films are supposed to be about car chases and good laughs, not animal rights.

I think it's really hard to outdo the original
and the fact everyone called him the Bandit
as opposed to just Cletus or Snowman seemed sacrelige