What did you find dumb about him trying to get away from a) his captors and b) vicious monsters who were tearing his well armed captors apart?
shareI see where OP is going - While he does wish to escape all that, he's also going away from the trained and armed soldiers who still stand a far better chance of keeping him alive than he does all on his lonesome... QED, I guess.
shareAnd how did that single Xeno get inside the locked area when the others didn't? They could have swarmed from the rear entrance and blocked the humans in before the attack happened.
shareWe only see one that destroys Burke but there could be a hundred for all we know. They can't get to the others though as he sealed off the door.
share[deleted]
The Xeno wasn't in the locked room, it was in the corridor that leads to not only Medical (the room Burke was in) and Operations (room where the Xeno's breached through the ceiling and floor.
The Xeno's attack after Hick's gets surprised.
Burke runs into the side room, locks everyone in Operations with the Xeno's.
Burke runs into Medical and locks that door as well.
He walks backwards through medical worried that the survivors will open the door to Medical.
As he's walking back he approaches the door leading to the corridor, and is snatched.
It's probable that there were infact multiple Xeno's in that corridor, don't forget we only really see a quick cut of Burke being nabbed by the Xeno and nothing else after. It's more than possible that behind that Xeno was a number of other Xenos waiting to get through the door.
As for the question why, it's simple really. Ripley made everyone aware as to what Burke did, he wouldn't get away with what he's done, even though he'd be going back to Gateway his life would be over for what happened on LV-426.
Putting myself in his shoes I too might've taken advantage of the situation, ran away and locked everyone in a room with hostile beings hoping they'd be killed off. Then if I somehow made it outside to the dropship I'd feed Bishop a story how everyone was ambushed and I was the only one to make it out alive (since Bishop wasn't there when Ripley revealed everything to the marines).