 They made people laugh. The more incongruous it is, the weirder the word is, the funnier people find it, with some constraints. If you make a really stupid word that has like no vowels in it or something, people don't find it funny. But if you make a reasonable word that's made up of unusual letters and sounds, the more unusual the letters and sounds are, the funnier people find it. The theory that incongruous non-words make you laugh works with real words too. I just think the word gazebo doesn't feel English.