it's hard to replace hardened tool steel , not without going to exotic metals and that would be out of the question.
soapstone,corian,ceramic would crumble to dust .
no matter how well you cnc machine molds they have to finished by hand.
than several days of testing-tweaking-testing-tweaking.polishing
than you deal with the quality of the bulk plastic,, and tweaking operating temperatures...
than you go thru QC and changes are requested and made ,, than more tweaking-testing,polishing,ect...
than the customer wants more changes,,, more tweaking , followed by more polishing and retesting.
eventually you get to production
btw ... aluminum can be about 7X more expensive than steel when buying it in large chunks like that