Wacky Races/WMG

Dick Dastardly cheats because... he's supposed to.
All cars, crews, and drivers in the race have a gimmick. Otherwise, it wouldn't be wacky enough. It's in the rules.

What's Dick's gimmick? Being the villain, of course.

He's allowed to take shortcuts and set up traps because he's the bad guy. If he won without trying to sabotage others, then he would be disqualified for cheating.
 * For the record, Peter Perfect has the gimmick of being an almost-normal racer. He's a presumptuous blowhard; aside from that and the stretching limbs/etc, his car is an actual racing car and his behavior is mostly that of an actual racer. He is permitted this because it makes the other racers look wackier.

Dick Dastardly cheats because... he's cursed.
Basically, he and Muttley are immortal, as long as they don't play by the rules, he gets to keep living. But the curse also stipulates he will forever humiliate himself. He cheats out of fear that if he does not, he'll die, though this is more subconscious. That's why he's been alive since World War I and would have appeared in Wacky Races Forever.

Red Max is the son of the World War I era Dick Dastardly.
He flies a WWI-era biplane which he has trouble getting off the ground, much less starting, much like the Vulture Squadron. He doesn't cheat, but he has used artillery to his advantage.

The universe itself hates Dick Dastardly.
He was stopped for a speeding ticket at one point.

Dick Dastardly is Sweet Tooth's grandfather.
My main basis for this theory is that both have a tendency to cause massive destruction in weaponized cars and their both villains, except Needles is more competent.

The Wacky Races are about as real as Professional Wrestling

 * That's why Dick never wins--he's the bad guy wrestler equivalent. He's supposed to lose. Moreover, his constantly setting traps may never take out all the other racers, but often does change who's in what position, making it easier for the person who's supposed to win the race to, well, win the race.

Dick Dastardly cheats because... The Mean Machine can't maintain a winning pace.
The Mean Machine seems to pass all the other divers multiple times during a race. Perhaps if it were to go that fast the whole race it would break down. So Dick stops to slow his opponents down so he can go at a pace at which the mean machine wont break down.

The Slag Brothers are from the same universe as The Flintstones and never appeared on that show.
It makes sense because... they're cavemen.