He needed to wage a war to make absolute sure he would seize control over senate and that he could simultaneously get rid of Jedi while remaining beyond their reach. Sure he sacrificed lives for his goal but he is Sith, he cares not for the means but for ends. And he wanted to rule it all (and have a worthy apprentice).
Meanwhile Rose Quartz Pink Diamond betrayed her kind, sacrificed countless of lives of her own subjects (while maintaining that she thought that all lives are precious) and brought grief to her mothers(?)/sister(?)/family so she… could live with humans on Earth? Which she could have simply done by establishing a colony (check), having an army (check) and telling other Diamonds that "No, I will not destroy the Earth". Sure they would be pissed but going by how other Diamonds grieve her death or "death" and how Blue i a flashback was essentially harsh but caring, I doubt they would do much.

The thing is, we know it all went, so hindsight is 20/20, but really, PD really did seem to think Blue and Yellow didn't give a shit about her or her colony, that she could never convince them, and that if she just disappeared, they'd up and leave the Earth alone.
By Pearl's reaction, they also definitely didn't think that they could or would corrupt everything like they did (maybe because they didn't think White would be involved?) – they thought the war was about to end already.

PD didn't think things through and fucked up huge time, but it seems much less to me that she had any intention of betraying her kind and fucking the Earth and the Crystal Gems up and more like she was just an immature, bratty teenager with waaaay too much power on her hands and maybe not so bright.

Basically, Yellow was right and Pink Diamond was 1000% not ready for a colony.