Chuckles
Let's not go into SF 'science' in movies and TV again, that's a subject that simply has no end.
(where DOES the oxygen on Tattoine come from? Frank Herbert went to the trouble to figure it out on Dune.)
Hmmm, never considered that, and you're making a valid point. As a 'desertified world', no herbage to make with the O2.
But, then again, only we hardcore, nit-picky, ETC, SF geeks notice that sort of stuff.