They charge $445 dollars for the bigger tank because it's another option they can make money on. Does it cost them $445, no probably like $25 more in extra plastic.
Yeah but you aren't just paying for the extra material. There is cost to engineer the tank factored in, the tooling to mold that tank, etc. Is it $445 more? oh hell no, but I'd bet its a lot more than $25.
For the record I'm in the "why isn't the 33 gal standard" camp. Its too bad there is essentially no aftermarket options for gassers (emissions regulations since the tank is part of the EVAP system) since lots of people buy a truck with a 23 gal tank.