Remember, when trying to roleplay/discuss/understand the Clans, you have to embrace the hypocrisy. They talk a big talk about avoiding wasteful practices, but they never pass up a chance to waste a resource, especially a human resource.
The Clans are weirdly wasteful of people. They don't want to give people artificial limbs organs or too advanced medical care because it's
"too expensive", ignoring the immense amount of resources sunk into every adult (and probably most children). Even the lowliest laborer represents untold sunken costs in food, clothing, training, etc. Even if you assume a fairly young retirement age (which is probably true for some laborers, less so for other castes), I've got to wonder how expensive an arm is that they'd consider it more useful than several years of labor.
It almost makes sense for training warriors - they want only the best of the best (it doesn't actually make sense, but it's almost justifiable). But for anyone else? Or, hell, adult warriors who are already trained and tested?
But it wouldn't be the Clans without weird hypocrisy.