AI (and computing technology in general) is an alien as it defies all wordly norms. It can have exact identical copies, can replicate, can exist everywhere, communicate across huge distance without time lapse, do huge work without time lapse, has no physical mass of it's own,, no respect for time, distance, mass and thinking work, not a living thing but can think.... Just the perfect alien creature qualities.
Why are they allowed to invade Earth? The business goals, of course. To get a temporary edge over the competitors, until they acquire the same. But once everyone has the same Ai, there is no going back. Ai has established itself through the weak channels that are filled with greed, that can bribed by giving toys (business edge), in return to the keys to the dominance of human race.