>>14892078
Articulated turrets will also take up some additional volume internally for their mechanisms and moreso externally with the weapons shunted out from the interior of the hull, additional mass, and with the way most space Mobile Armor fight- which is to say, as giant weaponized rocket ship fighters that zoom and boom the fuck out of the enemy- as well as the fact that large scale Minovsky particle beam weapons can generally be redirected just out of the lens in different directions, do not actually add very much versus a fixed mount with a beam redirection arc or a gimbal.
Of course, the 'internal-external volume' part falls apart a bit when space Mobile Armor- like these >>14892250 - also generally have big fuckoff blades or ship-mangling claws to physically shear bits of the enemy off in a pass or grapple, and articulated turrets are hardly so complex or decadent as Newtype guided bits & funnels or their Oldtype INCOM equivalents. But you don't see turrets very often on Mobile Armor because they're not necessary or are supplanted by arrangements that aim even more freely.
>>14892135
>But then why use them to fight instead of a smaller space fighter that's harder to hit? I just can't really see the appeal.
The Earth Federation followed both of these lines of thought to a T. The FF-S3 Sabrefish exemplifies the ethic you described. They got *fucked* as soon as the war started, with their military strength cut to shreds in a week by the Principality of Zeon's Zaku II mobile suits. Somewhere around a half of the earth is occupied in a subsequent ground invasion, in which the Federation's Type 61 battle tanks similarly get their shit fucked up.
http://gundam.wikia.com/wiki/FF-S3_Saberfish
http://gundam.wikia.com/wiki/MS-06_Zaku_II
http://gundam.wikia.com/wiki/Type_61_Tank
The thing about Mobile Suits is that the AMBAC system- their ability to swing their thruster decked limbs around like giant externalized reaction wheels- gives them *bullshit* mobility in space, with dime turns and easy bake thruster-assisted momentum changes, and being a gigantic man-shaped fighting machine with handheld armaments means 'internal volume' is not something you worry about in terms of armament anymore. It has a 120mm automatic cannon; whether this means it has a bore diameter of 120mm or indicates something else entirely and fires a smaller cannon shell, some saying 76mm like a gigantic AK-47, is immaterial. It will also generally have a big fuckoff rocket of some kind that can dump battleship class munitions into a space ship at medium to short range. And it is built out of 'super-hard steel alloy'- Gundam is from the very late '70s, so rolled & cast homogenous armor are still the order of the day with composite armor being obscure if not unknown, essentially a Soviet affair until the West developed Chobham armor, at which point it was transplanted into Gundam and even using that name- which will no-sell most conventional, non-gigantic weapons, which is to say anything short of a couple of MBT shots or guided missiles, until the Earth Federation develops its own mobile suits and anti-MS weapons. This chunky deflective armor arrangement later proves a problem when the Federation gets a leg-up on particle beam weapons, which simply don't give a shit about armor that isn't specifically treated to deflect particle beams, but again, that comes much later.