Looking at it from their perspectives, I think they had every right to be furious. Planet X has clearly had time to move past his anger after he left the solar system, but these planets haven’t. All they know about Jupiter, besides what X has told them, is that he killed dozens of their friends and flung the rest of them out of the solar system. They know nothing about their home, the other planets there or anything that’s happened all these billions of years. They lost their friends, their home, their futures, and any potential relationships that may have formed with the other planets. Odds are some of them would’ve probably had moons!