They’re stored to ship complete products, if you take a seat from storage for repairs then you’re stuck with the rest of the chair without a seat.
Herman Miller also makes premium chairs so that explains why it’s so much more expensive, but I’m sure you can find brands with parts available that are cheaper, just not as cheap as whatever you’re buying now and there’s a good reason for that.
They’re stored to ship complete products, if you take a seat from storage for repairs then you’re stuck with the rest of the chair without a seat.
Herman Miller also makes premium chairs so that explains why it’s so much more expensive, but I’m sure you can find brands with parts available that are cheaper, just not as cheap as whatever you’re buying now and there’s a good reason for that.