It's not just troops, but the building themselves. Armor factory costs 15000 florins in MTW2 but most factions don't even have any unit that can use it, save for general's bodyguards. Even the 10000 florin second highest upgrade isn't used much by most factions. Also, the top line buildings are so expensive and some don't even unlock new units, just give one or two units +1 experience. The Alchemy line, IIRC, upgrades only the melee ability of gunpowder units. The top tavern buildings only give 5% additional happiness and the costs ramp up as well. The highest market building is so expensive but gives such a crappy increase in income. I could go on and on, but there's just too many useless buildings, especially at the top of the tech tree.

The same happens with units. I think the Feudal Dismounted Knights cost 570. The Chivalric version is slightly more expensive, gives 1 to attack (or maybe armor?), but requires a higher castle level and additional buildings. What's the point of that unit?