I think the weapons you're talking about that have over 200 reach are typically lances and spears. While those have high reach on paper, you can only thrust them at one direction, they have low attack speed, and have dead-zones that can sometimes render thrusts harmless.These are easy to use against slow moving ground units where you can anticipate their movements; facing fast moving khuzait mounted units though, its often hard to one shot them with thrusts and couching takes too long. Voulges, menavlion and glaives on the other hand, while not having 200+ reach, they still have roughly 160+ reach. Not only that, but you can swing them, allowing them to literally use more of weapon's length to attack.
With the way cav-on-cav melee battles usually happen, you kill enemy cavalry that are often charging towards you, hitting enemies running away from you just significantly reduces your damage. So say you're attacking an enemy that is charging towards you, landing a clean thrust on a moving target takes extreme precision and luck, since you both have the same angles of attack, so either you hit first, or you out-reach your enemy. Using a swinging polearm however, allows you to attack from angles that make it hard for khuzait lancers to hit you back with their lances. Not only that, I have never encountered an attack deadzone with my voulge, whenever my attack connnects, it always deals 100+ damage, unlike spears and lances that can't effectively hit enemies that are too close to you, or when couched attacks just miraculously deal 0 damage.
Dealing against horse archers is like committing war crimes, you're bascially killing unarmed enemy combatants.So ease of use is important, if I can consistently dish out damage, with low rates of failure, that's the weapon you should be using and swinging polearms fit that description for me. I just find thrusting polearms hard to use against fast moving khuzait mounted units. I know I'm just bad at lances and spears, but for other people who are having a tough time against these pesky khuzaits, polearms are your go-to weapons, use lances, spears, voulges, menavlions, glaives, just any polearm with high reach. Make your attacks count and disengage whenever things get ugly.