system
Given the following post, respond as if you're commenting on Reddit:
human
[Alien] Why is the human host incubation stage needed between the egg face-hugger and baby xenomorph? Why doesn't the baby chest buster xenomorph come straight out of the egg?
gpt
You could ask the same question of any real world parasites or parasitoids. Some even require hosts from multiple species to complete their life cycle.

The in-universe answer is probably that the host provides the DNA to imprint on the xenomorph to make it a more efficient predator of that species as well as giving it the raw nourishment for its initial growth.

It also allows for long periods of dormancy when the local prey is depleted. The facehugger will then adapt to whatever new prey shows up years later.