I think using heavy materials for any environment isn't the smartest idea. From shelving weight to shipping, it just doesn't add up. Maybe a sense of premium but no one hefts their display bases around screeching "look how heavy it is, it's worth so much". It's the same stupid **** with InArt using real wood and metal for their Joker base. It's a giant publicity stunt to imbibe "value".
But I suspect that for manufacturing somewhere along the line, polyresin is cheaper than making the metal molds for plastics, which is why it ends up being used more often.
In the early 2000s we were doing a lot with rotocast stuff, like the 12" Toybiz figures. I'm surprised that isn't used more commonly for light weight, larger pieces anymore.