Incase nobody knew this already I heard this from Screamscape. Speculation: I’m guessing the choice to let Kodos do all the talking may stem from the fact that Kodos is voiced by Dan Castellaneta and Kang is voiced by Harry Shearer. If you go back to the story behind the creation of The Simpsons ride, it has been said many times that Harry Shearer opted to not work with Universal on the project, while all the other voice talent joined on. As a result all of the characters that Harry Shearer voices either are not present in the attraction, or remain silent. In addition to Kang that long list includes: Mr. Burns, Smithers, Ned Flanders, Reverend Lovejoy, Kent Brockman, Dr. Hibbert, Lenny, Principal Skinner, as well as Otto.