Re: Why is it
A couple reasons.
Gotta make dough on spare parts and people will pay it.....
Legitimate stocking, handling, hassle, of spare parts - this is not minor. I've been on the procuring end - depending on the items, sometimes the distributor can negotiate from strength and get free spares - say 50 units worth of spare parts (or something) if they order 50,000 (or whatever).
Most companies will treat spare parts as a profit center, not a goodwill counter.
Now as for the dealers of bike parts....some like thatsdax look pretty OK. An entire carb? What? $22? That's like 0.000001 euros.