From a practical/evolutionary survival perspective:
- Crawling out the esophagus would've meant being exposed to the host's own teeth.
- Crawling out the esophagus might mean leaving the host alive, and injured, and dangerous.
- Killing the host ensure the host couldn't kill the emergent organism.
- Killing the host in spectacular fashion momentarily
shocked and paralyzed the rest of the Nostromo's crew... thus
facilitating its escape when it was most vulnerable.
From the symbolic process perspective:
Because it graphically reinforces the process of occult self-annihilation in the context of the birth of emergent cultural abomination.
(Occult simply means that which is hidden (cult) from sight (ocular))
The process is symbolically illustrated throughout the series.
Observe that, in the original Alien, on the self-destruct panel of the Nostromo is a "Padme" button.
Padme is Sanskrit for the lotus flower. The lotus flower symbolizes the promise of enlightenment in Eastern ideologies - for example:
"In Hinduism, the lotus flower is very significant as it relates to the sacred Padma lotus, and is associated with numerous gods, including Vishnu, Lakshmi and Brahma. In many ancient works of art, the gods are depicted with lotus flowers as they represent purity and divinity"
The obvious In-universe parallel to the Padma Lotus is the tempting, but deadly face-hugger-spewing, egg.
There was never any guarantee (aside from monetary inducements) that the actual state of existence confired upon the "enlightened" would be healthy for the confirmant crew of the Nostromo, deep in the heart of darkness... of Space; and that fact is borne out by the consummate fate of first the infected captain, and then his entire crew, each cocooned into their own temporal hells - including Ripley who ultimately plunged into the furnace in Alien3.
As Mother revealed -- the crew was always expendable in the context of the Corporation's secret desire to achieve its collective, self-worshiping, goal.
Observe Ash's quaint confession
and how, although the Weyland-Yutani Military Industrial corporate mind knew the likely outcome - at best it didn't care, and at worst they derived a sadistic pleasure from the inhumane demise of the expendable, inferior, livestock within their purview.
And the more horrifically and paralytically shock-and-awe-inducing the emergent bio-weapon... the better!