mainly "cheap" to make, butt hats the nature of "plastics" (polymers) they can and do break quite easily, the newer stuff is much tougher these days but look at ANY old gun that has whatever form of plastic grips of the era , and they are broken, chipped or the escutcheons 'pulled;' through or busted out,no matter what make or model of firearm...............lots of guys here on the Ruger forum, making grips to whatever YOU may want ,materials as well as sizes.......you want 'rosewood, then go for it.........
and you can always call the factory or any of the national grip makers out there. We see them at the gun shows locally, on any given weekend........