The reason that I think Uncle Bud is being so nice to Jack and Isadora is because he has plans of how to get back to Earth.
Uncle Bud will probably build some type of space ship .
2. He will take over the Queen now that he is the King of Skreepia and make them obey him and do what ever he says. This could be possibal because you know what type of mind that he has and can think up some weird things.
3. The "King" of Uurth could take over the Skreep ship over and find a way home so that he could save them all from being tortured by aliens.
4. Uncle Bud will unleash beast 11 so that the beast will eat all the skreeps so that Uncle bud can take over.
Those are some reasons that I think will work so they can get back to Uurth.