We wrote:Tau are a top tier army, so
GW raises the price on anything good to make more money.
Old armies are cheaper and old players own a lot of them so
GW makes them suck. This encourages players to buy the newer, more expensive armies and units.
Maybe take the tinfoil hat off? Everything
GW makes is expensive, and newer kits are more expensive than older ones. There's no greater conspiracy than that, because there's plenty of examples of new, expensive kits that are crap rules wise.