Well, thats one thing u should have realised long time ago. Logitech just uses cheapest parts to build theyr products - and then sets pretty high prices on them. And it doesnt suprise me that its all plastic. Thats just what u get if u decide to go with logitech.
Same thing with logitech speakers, they are all utter shit ... why are people even buying them? ...
Logitech is cheap and overrated. Thats all.
Edit: I remember i saw one news article somewhere and there were said that if u see a logitech mouse with a pricetag of like um ... 20€ or so - then it probably took logitech 5€ to build this. Parts and building process in total.