Never in my life have I encountered an instance where I thought there was any real reason to use something other than PVC. Cheaper, paint apps for it tend to be more colorful, quality is much better because of how refined the sculpts can be, and the quality control seems to be more straight forward. All the other stuff is just heavier and...yeah that's it.
Jerry Macaluso from PCS explained this once. He believes that PVC is a superior material. It gives better details. The biggest advantage is that since all pieces come from the mold exactly like each other they can use copper paint masks on the figures instead of having a person paint every detail.
The reason they often have a plastic look is that instead of using paint for skintones or whatever the predominant color is they usually inject that color into the mold.
The downside according to him however was that for anything over 12 inches, the price for the molds quickly skyrocket making in infeasible for 1:4 scale pieces.