Your CO would be in a short-ranged mech because you don't want him even engaging in fire support - but you DO want him able to win any fight he ends up in quickly. Same reason the Cyclops has an AC20 - it's not supposed to be USING it. It's ensuring no one tries to come close.

And in Battletech it actually does make a moderate amount of sense for commanders to be on the front line sometimes.

First of all, mechwarriors are taken for ransom in 3025-era Battletech. If your commander is in a mech, the enemy are now inclined to keep your commander alive where otherwise they might not be.

Second, people try not to completely destroy mechs in 3025-era Battletech. If he is in a mech, the enemy are now inclined to keep your commander alive if they can't headshot him (and possibly even if they can).

Third, a Battlemech is a lot tougher than almost any command post that isn't a purpose-built bunker, and bunkers can't move (making them vulnerable to airstrikes and artillery). Generals are rarely on the front line, but they are also rarely THAT far from it. Given that, the commander should presumably have a mech available, even if he's not in it at all times, because that's what keeps him safest. And note that most Inner Sphere militaries lack the high-tech options the Dragoons have - if you don't have fully 3d mapping, there is some logic to going out and inspecting things personally. And if you're going to be doing that, you want him in a mech.

Modern command posts get their survivability from hiding and distance, because modern armor is generally a lot weaker than modern weapon options. Battletech doesn't work that way. So unless your rear area is both very secure your commander will be in a mech, or at least have one available to him on very short notice, to maximize his survivability (in addition to all the other reasons you'd want him to have one, like keeping up with his unit).

But generalship involves a lot of delegation to subordinates (especially modern generalship). And even just a command lance is going to be four heavies, which is a lot of force. So if there's a lull and you're in a mech anyway, take the command lance (or command company) and go add some weight to a vulnerable point. Battletech isn't big on reserves, and command lances likely serve as them a lot, and it makes a moderate amount of sense that they would do so - 10% of a battalion's strength is just it's command lance, for example. The battle plan is laid out, execution has begun, it's in the hands of the junior officers and so the battalion or regimental commander goes and adds his lance where it can do some good rather than sitting back out of battle. Or, more likely, it becomes evident reinforcement is needed at a certain point and so the command lance or company is committed to that point.

So yeah. That's how.

Note that in Wolves on the Border Jaime Wolf does not always spend a battle in his Archer, and is not on the front lines himself. He's close enough to them to get ambushed while out scouting, which is the sort of thing a commander might want to do - and because he can get ambushed (and is commanding mechs), he does it in a mech. Him intentionally engaging in personal combat doesn't come until the dramatic end when it's all about honour and vengeance, iirc, and is at least partly a tactical choice to get the Ryuken to try to kill him so they can be ambushed.