system
Given the following post, respond as if you're commenting on Reddit:
human
[Animorphs] Why don't the Yerks start their invasion of Earth hot?

I get that they prefer the slow, Invasion of the Body Snatchers-style takeover, but it seems to me that they have more than enough resources/manpower to run a quick, effective campaign. 

It looks like European settlers trying to politically coup the Iroquois.
gpt
It’s revealed that the Visser (the Yeerk form of General or Warlord) who had discovered Earth and first infiltrated the society had fallen in love with another Yeerk, and using their hosts, reproduced sexually instead of the normal method of fission, where a Yeerk would die to create hundreds of offspring from its corpse. The Yeerk who would be known as Visser One fell in love with the children (there were twins), and feared deeply that an active hot invasion involving open warfare would result in the death of the children. As such, the Visser organized a valid way of covert infiltration that came to be known as the Sharing, a social organization that was in truth a front for discovering voluntary hosts. With multiple recordings to serve as proof-of-concept, Visser One showed this to the Yeerk Ruling Body, the Council of Thirteen.

Though other Warlords such as Visser Three wanted open warfare, the Council overruled him and kept the covert infiltration as the method of warfare due to Visser One’s proof and fears that open warfare would result in an escalated war where their main enemies, the Andalites, would destroy the new Host race, the Humans, just like they did to the Hork-Bajir once they discovered how important the Humans were to the Yeerks. The humans were special not because they were physically exceptional, but because there were so many of them. There are millions of Andalites, a powerful galactic power. There are billions of humans. Keeping this race and its importance secret was paramount.

Ultimately, both Visser Three and the Council were correct. When Visser Three started open warfare, his forces dominated Earths’ military and he quickly set up Yeerk pools to get thousands of hosts infested at a time. At the same time, the Andalites had caught up to the Yeerk’s plans and indeed decided to destroy all humans to keep the Yeerks from such a great victory by igniting Earth’s atmosphere with their weapons, killing the vast majority of humans. Only the Animorphs kept the Andalites from destroying humanity at the end of the war.