"Because if NOTHING else, Gilgamesh was your best friend! He inspired a bunch of humans and spirits! There's an entire legacy that's been erased, which is exactly what that idiot illusion witch wanted!

And, yeah, there's some selfish shit to what we want because we want our sisters and dad back, but there's also good it's going to bring to the world! Our pops and Gina and Trena all did stuff for mankind and while we may both not really care what happens to mankind, it's not like we're actively antagonistic to them either!"