How many people out there have the money to go buy a brand new engine from the manufacturer? Genuine Nissan and Toyota parts are a complete rip off.
And its not overly viable anyway, people aiming for big power generally get everything machined like new.
And if you're aiming for big power, majority of the engine is going to get replaced with forged internals, which means half the money on that engine goes down the drain and could have been better spent on something like a stroker kit.
Obviously its a bit different when it comes down to rotaries though..as once a housing is warped its useless.