The comic tells a different story than the show.
Dragon Ball Super is over. The series finale of the show aired just a few weeks ago, and fans' heads are still spinning from the conclusion. After Goku and Jiren's battle concludes, Frieza appears to save the day along with Android 17. Both characters have long been considered villains, so it was amazing to see them ultimately save the good guys, and their entire universe. Viewers who are eager for more Dragon Ball Super content may have to wait until the live tour taking place in the US and Canada, or even worse, they may have to wait until animated movie drops in December. There is one other method fans have though, and that's to read the manga, or Japanese comic, in which the show originates from.
A new chapter of the manga was released this week, and it changes some minor details from the show and gives insight into why Frieza didn't just betray everyone from the beginning. In the comic, Frieza teams up with Frost momentarily, but later betrays him to save his own universe. After the unexpected move, Frieza reveals to Gohan his true intentions.
“Save your gratitude,” Freeza tells Gohan. “It’s all for naught unless we win and survive. That’s when I’ll deal with you Saiyans myself.” So nobody is allowed to kill the famed Saiyans except for him. What a greedy villain.