(i'm looking at you, mechwarrior series with your 900m max range '''long-range missiles''')
Okay so a lot of the ranges come from Battletech, and the weapon ranges there in BT are mostly just for 'balance' reasons. Though it gets better, the in-universe reason why the weapon ranges are the way they are is because the battlemechs (and tanks, and everything else) have so much EW equipment as standard that it makes combat from out farther than the normal ranges a crapshoot, and pretty much the only people who can shoot out farther than normal ranges are typically named characters who are 0/0 gods amongst men (the typical mech/aero pilot is 4/5, 3/4 if they're a clanner, the lower the numbers, the better.). Though a lot of the novels stretch out what is standard range for the sake of better writing.
Welcome to the mess that is BT's version of grimdark, it so desperately wants to be grimdark like it's more successful brother in 40k, but it falls over and explodes half way through the race because the guys at FASA came up with a setting with the intent on being very grounded first, and had to spend a lot of time trying to justify how the universe ended up the way it did by way of indirectly giving the roman empire a reach around. Which yeah, so much of the universe's premise is pretty much revolves around the fall of the space roman empire (The Star League) causing the universe to go to shit.
A lot of people who write overall setting lore for the Battletech universe don't exactly know how mass production or logistics work, so much that one of the very first retcons was introducing "limited" battlemech production still happening throughout the succession wars. Another fun one that was quickly redacted, was the quoted number of jumpships (the FTL transportation for the universe) being at around 5,000-6,000, except that fell apart as the Invader-class jumpship (most common jumpship) with all it's docking ports filled with Mule-class dropships (most common cargo hauler dropship) had the effective cargo capacity of one normal 21st century blue water container ship. There is no way that only 5-6k jumpships was ferrying all that cargo for all the populated planets that is pushing 7 or 6 digits in total, a lot of those worlds being just as or close enough populated as Terra is.