system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why is infantry combat so undeveloped?

**Ship Delivery Methods**

Torpedoes are frequently seen as being able to penetrate shields, and even early ones like those carried by the NX-01 are large enough to carry a person with a decent amount of room to spare. It seems like one species or another *koff ~~Klingons~~ koff* would have added a compact inertial dampener and some variety of high-speed release system to deliver a space-suited trooper into corridors and near vital systems. Alternately, shuttlecraft could "drop" troopers onto the hull of a ship with some type of combat airlock, to penetrate outer plating and perform sapping/sabotage if not outright killing the crew and taking control. Given the lack of point defenses or onboard marine complement on most vessels (The NX-01 circa Xindi Crisis excepted), this seems like a valid strategy just with the basic infantry combat equipment already present.

**Additional Equipment**

*Subsection 1: Weapon Types*

There seems a very distinct lack of weapon diversity. Beyond the variations each species makes, there are only two common weapon types, handheld pistol-types and two-handed carbine-types. Neither seems terribly suited for long-range engagements, or any type of armored unit. Weapons like sniper rifles or SMGs are most notably absent. The former's use would be obvious (although designated marksmen are also rarely seen). The latter may be useful against shielded units; it would appear that shields are very proficient at stopping slow-firing, energetic, high-impact shots (see every ship engagement of frigate class up) but seem poor at protecting against large quantities of low-impact projectiles (see engagements with Suliban Cloak-Swarms). Ergo, weapons with a high rate of fire may be useful for taking down shielded units like the Xindi deployed. Also absent are larger "caliber" automatics, or equivalents to a modern LMG. This may be related to the notable lack of armored units, discussed below.
 
*Subsection 2: Armor*

Armored units are almost never seen beyond apparently-useless body armor worn by MACO Troopers and most Klingons in anything even approaching a combat role. Seen even less (and possibly of more importance) are armored space suits-or, perhaps more accurately, vacuum combat suits, which would greatly expand the feasible range of vacuum activities (see section 1). For those in planetary combat roles, full-body armor suits with mechanized movement assist could act as both a heavy-weapons, armor, or advanced equipment platform and, if fast enough, act in a search-and-destroy capacity for units that evade the detection equipment portable by standard combat units to help prevent infiltration, sappers, or commando teams from being effective. Planetary forces in particular are woefully lacking in such fire support or even planetary bombardment (even though they are capable of it; Janeway threatens a troublesome industrialist that *Voyager* could vaporize his entire office building) to prevent armored offensives. What's more, the fabrication cost would be exceedingly low for the tech level the Federation possesses.

*Subsection 3: Automated, Remote, and Mechanized Tools*

Where are all the drones? A remote unit, utilizing the same relatively simple mechanical principles as Data uses to move, would be relatively cheap to fabricate (Data built a basic version of one _complete with positronic brain_ no less) and possibly faster, more durable, stronger and more accurate than a human trooper, potentially controlled by a ship's computer, advanced AI, or even completely autonomous with a simple positronic brain designed to take orders and carry them out, optimized for firmware and tactics. Such units are easily made fail-safe, and as the Borg show, are potentially quite formidable if their main weakness, their wetware component, is removed. Other than automated marines or troopers, simpler automatic targeting subroutines could be installed on small turrets mounted on a mobile armor unit or in corridors as an anti-boarding measure.

 

SO WHY THE HELL IS NONE OF IT USED?!
gpt
Because ship to orbit phasers can pick out individual houses and vaporize them with little to no damage to the surrounding structures. 

Also, because infantry combat is a dirty, ugly, messy business that doesn't contribute meaningfully to interstellar affairs. The only cultures that go for it are honor based ones or the ones that want actual domination instead of just cultural hegemony.