I think its the background bit that prevents a totally civilian career from working. One of the gaps and something
I obliquely touched on here in this thread about the other entities that would have to decide on MilGov or CivGov. Is that you could have a federal agent who never enters the military and is stuck in the US or maybe overseas with what is left of US government representation.
However, in most of the background material that is presented in the core rule books. By 1997 in the US at least the Selective Service has been brought back from the dead. Remember in 1984 when the rules were written the Selective Service Act was restarted by Jimmy Carter in 1979 in response to the Soviet invasion of Afghanistan. So that meant everyone who was 18-26 in 1979 had to register or lose any federal benefits. So the authors assumed it would have been maintained, instead of let to atrophy like it has in real life. So that when WW3 starts, the draft would have been reinstated as the war starts.
Since I have only done character creation under V2.0 rules, I can't say if V1.0 is different. Always assumed the "War Term/War Starts" roll is the draft roll for civilians. We had a few folks develop civilian careers, I think the best I remember was a 3 term doctor who then had the war start and the lost the roll for that last term for whether the war started.
I always felt it was unfair that the career ends for folks drafted from civilian careers would stop any promotions so they are basically very junior officers or very junior enlisted folks when the war starts. So we had house ruled that you create a civilian and the war starts, you had promotions rolls you have equivalent to how many terms you had on the record sheet before the war starts. However, fail a promotion that is where you stopped at; it was an attempt to balance out things for some of our players that pointed out things like battlefield promotions or even folks "buying" their way in because of previous life experiences the military gave promotions to a certain level.
I would also note that per the character creation rules, you don't have to stay full time military and could pretend your character is a National Guard or Reservist who drills actively. So you could do a term or two in the military and then switch to a civilian career only to see yourself activated due to the war starting. Which again the rules are strict about, but can be house ruled to say that once you selected say armor in your first term. When the war starts you can't magically jump to become a pilot; unless you did all the pre-reqs. So you would have to do your war term in armor with the promotions.
As to the rank, we never played that much amongst the group with rank; only when the GM's called for it in dealing with NPCs. Otherwise, the only real reason for rank is what you had as "spending" cash prior to the start of the game to buy equipment. Since it was 5k multiplied by number of terms for an enlisted guy and 10k with the same multiplier for an officer.
As to the tactics question as a PC. Really? I used to be in the military and was given some basic weapons handling skills and some basic self-defense skills as well as how to handle myself while on patrol on a flight line with the military. Yet, I didn't do it that often in real life and our training was something akin to about every 2-3 years to learn how to shoot and how to use some basic forms of cover and concealment while defending the flight line. So there is no real need to know combat tactics in a game like T2k. Reverse the question in a game like Shadowrun, do you really need to know tactics of how to be a hacker to understand what you are doing jacking in to the net in that game? What about tactics of being a Paladin in some fantasy game like DCC or DnD? Most of this is going to be good story telling and a beneficial GM to say what could work and might not work, let alone hand wave away maybe a bad roll by the PC or even the GM to allow the game to run well.
As to the diversity of the game. That is going to be complicated discussion and can really go sideways fast. There has been a discussion, IMHO, with in the TTRPG communities on a whole about how diversity can or can not work well; for at least the last decade. Everything from how DnD and other fantasy works could do better about allowing various races like Orcs and Elves and such live without straight animosity. Even some op-eds or long form essays in various magazines about how fantasy tropes of racial biases were born from colonialism. Similarly, trying to get more women involved or even allowing LGBTQ+ communities to exist without being a Mary Sue or not an overt stereotype in the campaign has been difficult. There is nothing, in the rules that says you can't be a woman or that you can't be LGBTQ+. That should be completely up to what the GM and the Players want to play or how to play it.
As to my problems recruiting players to game T2k or its derivative Merc2k on the table. Just been how old the rules are and how crunchy some of the rules are in doing things like trying to figure out combat, movement, and some other important things like scrounging or distilling. I have tried to scale in those rules as we going to get further into the campaign on over to just saying that even though the rules are old there are still active players in AD&D campaigns still using AD&D rules that were published only a few years before even T2k was published.
Finally, I think it is just that where I am living right now the two most popular games systems are DnD and Pathfinder, with Shadowrun or Mutants and Masterminds a very close third or fourth (depending on the polling). Anything else is forgotten about or poo'd on by folks. Heck I have tried to get a GURPS game going set in near modern era of mercenaries and do something like "The expendables" like campaign. Only to see no bites because it isn't the cool thing on the shelf that you can see at any FLGS or at Barnes and Noble.