system
Given the following post, respond as if you're commenting on Reddit:
human
[Starcraft] Why don't Terran tanks have machine gunners?

Why would the Terrans decide to take off a very necessary part of the tank? The top mounted machine gun has always been a staple in tank manufacturing and always been a necessity for close combat engagement. Why would they remove this very useful piece technology?
gpt
1) It's more expensive - it's an extra gun, extra targeting systems, probably needs an extra gunner riding in the tank which means it needs to be a little roomier on the inside and have a more robust life-support system to keep another guy breathing when the tank is out on Fuck You Hell Moon, which is another couple factors that might compromise the tank's structure or armor if they're not bulked up... The units you commonly see fabricated and deployed are all in a delicate sweet spot between being as cheap as possible while still very effective.

2) The seige tank really shines as a heavy yet mobile artillery piece, as part of a combined-arms force. When it's deployed and fulfilling its role as long-ranged fire support as well as possible, the machine gun will not be a useful addition. COULD it come in useful in a pinch? Yes. But see point 1) - if it's not totally necessary, strip it out and make a cheaper tank.

3) Infantry isn't what it used to be. Back in the oldest days of warfare when soldiers ran around with just shirts or flimsy un-powered armor and would commonly go down in one shot, it was a huge benefit for an armored vehicle to have machine guns and be able to just roll up and unload on infantry. Now, with man-portable gauss rifles, an 'armored vehicle' doesn't offer the kind of protection against infantry that it used to. And, with man-portable powered armor that can withstand certain explosive tank shells, a tank is strongly incentivized to rely on its *longer*-ranged weaponry instead of trying to compete in close combat.

4) You show me a machine gun in a fixed position like you'd find on an old earth tank, I'll show you an eight-foot tall alien warrior in his own power armor who will run straight towards it at forty kph, catch every bullet in its energy shields, and cut through its armor with a fucking laser sword.