The main reason for all the plastic stocks by makers is simply cost. They are cheaper to make and cheaper for the buyer to buy.

Sad for beautiful walnut and blued steel.

I have my Mauser M03, one of them in plastic and not so nicely blued, supposedly less prone to rust etc. But if I could I would have all of those calibres and cartridges in lustrous blued steel and fantastic walnut, takedown M98.

The main reason it is what it is? Cost.