But the only reason that people don't do a thing is that they can't or they won't. So since we know that the Mi Go could eliminate Earth at any time, they won't for some reason. So something is staying their hand.
2) I'm not saying it is the Mi Go's true agenda, I'm saying that the Union doesn't know what the Mi Go's true agenda is, and there's probably several competing ideas on it. Both within the public and within the Military. I'm saying that it's better to have more different ideas be possibly be true at the same time than to have less. It's even good for setting realism purposes to have ideas that float around that people subscribe to even though they're demonstrably false in some way. We have a pretty solid grasp of exactly why Hurricanes do their thing, but people still blame the gays and women voting and other things for them.
3) The Anti-Spiral plan might just be a weird Xanatos Gambit for all we know. "Master This And You Can Have It!" stuff. I mean shit, Cthulhu thought that it was a reasonable enough plan to uplift proto-humans into ageless Deep Ones so that they could stand guardian over him for millions and millions of years as a way to avoid some sort of problem he was having at the time. These cosmic creatures do not think small.
Here's some options for why the Mi Go might want to do what they do:
- Secret Miners: The Mi Go at Earth are a rebel/splinter fleet(s) that wants to recover the resources of Earth as secretively as possible, so they never contact the home empire.
- Foundation Gambit: The Mi Go know that their empire will crumble within a billion years, and they need to ensure a galactic successor. Possibly because they are facing some sort of heinous enemy that will need to be battled even after they're gone, possibly just because they think the universe needs to be full of biological life. Anything really.
- Anti-Spiral Gambit: Interstellar races without the self-discipline and fortitude will bring accidental destruction to their species, space, galaxy, or even the whole universe in some way. To prevent this, the Mi Go apply "light" suppression to all other species that they find, and those that last are considered to be most likely to not accidentally destroy everything. For the same reasons that even Good aligned DnD characters take magic items out of the hands of the peasants until they're higher level, the Mi Go don't let you just spread everywhere until you really know what you're doing.
- Shadows Gambit: The Mi Go think that a species (and possibly the universe as a whole) can only unlock its full potential through continual strife and survival of the fittest. Even though they understand that too much strife causes extinction, they still fight all the time to keep things "moving forward", or to keep them "interesting", or because their dark god MiGoWeh demands it.
- Proxy Warfare Theory: The Mi Go conduct battles and operations in the Earth area because somehow that is symbolic to them of a greater conflict elsewhere. Something like The Cold War, or A Taste of Armageddon, or the Ellimist / Crayak battle.
- Predator Training Grounds Theory: The Mi Go don't want anything but operational experience from the Earth. Mi Go that die while doing something in the Earth area are considered to have not been good enough in the first place. The whole system is one giant training ground to them, and keeping it full of hazards is what they intend.