Continuity mistake: Spaceball-1 is using a blue tractor beam to bring in Vespa's car, but when Barf opens the roof to rescue the girls, the blue light is nowhere to be seen.
Continuity mistake: When Lone Starr 'knocks out' the guard who was shaving, the guard's grey key card falls to his side, but in the next shot the key card is laying on his butt. (01:11:50)
Continuity mistake: When Helmet is trying to hit Lone Starr with his Schwartz but Lone Starr is holding his head, you can easily tell that Helmet's Schwartz is made shorter so it won't hit Lone Starr.
Answer: The Spaceballs are a race of bullies, they only pick on planets they know have no defense, like Druidia. Yogart, like Yoda, was a very powerful being with mystic powers, While the planet of the Apes were highly intelligent and were most likely able to out smart a race of idiots.