Theres that and for the gonarch they needed a way for you to be trapped in there with it until you defeated it, then for a path to open up after killing it.
Uh huh, Valve does that a lot. There are certain gates that prevent you from progressing until you do something or a sequence has been completed (Dog moving the dropship out of the way after the Strider fight, Alyx opening certain doors only after certain sequences, etc.) The Gonarch exploding was no different, though it could have done well to explain why it exploded. Maybe its sack is filled wish some sort of combustible nutrient or gas?
Love your title…
On topic, the exploson might have been a protecton thing for it’s young, even though they pointlessly attack you anyway…
It was full of acid stuff, that it mortared at the player.
In which case, let’s hear it begin to sizzle right before it goes kablooey.
Eat my dick.
Surely you would come off worse in that situation?
extremely chemically unstable jizz?
ACIDIC JIZZ
I was kidding man, no offense meant. Sorry, Winged One.
He wasn’t offended. He just offered you to partake in devouring his manhood. 
On Topic: Isn’t the idea of “acidic jizz” a little…out there? I mean, sure it sounds awesome on paper but once you get ingame you are like “Whoa…he just jizzed on me”
Really On Topic: As for the Gonarch asploding. The fluid in the body could have violently reacted with the bullets and possible explosive weapons you use on it. Some things don’t react well with others. Like you could say that the Garg explodes because whatever it uses to fuel the fire that comes out of its hands could have been detonated.
Well, actually, most things usually explode when encountering extremely high voltage and especially air strikes.
Headcrabs are like sperm. The gonarch’s testicle spews headcrabs like sperm. And what do sperm do? They “couple” with the ovum – you – to create a new creature.
Simple.
For every question there is a simple, short, understandable, incorrect answer.
Before bashing the birthing testicle, one must consider the implications the HL2 physics system will have on said testicle. Surely it will be a wonderous site to behold.
On-topic: The only relevant suggestion for the Gonarch should be “please use jigglebones because we all love gigantic jiggling sacks.” In fact, I’m confident the BM Devs already have this implemented, they know what they doing.
Off-topic:
Winged One’s title should probable read “I tried sucking Raminator’s dick and asked Slyr to Eat my dick and all I got was this stupid user title” amirite?
Still saying some off topic things heh.
Yeah, where were you going with this ?
I have a small request, can you please not put hair on the Gonarchs testy? I think I’d be scared for the rest of my short life.
Dooood, put hair on it’s sack! DO EET.
They could do a similar thing to the hair that was on the black headcrabs in HL2 on the sack of the Gonarch, come to think of it.