It's called RNG. You aren't guaranteed to get one item/fragment compared to another item/fragment.

I also used to play this online game 'Great Plates'. http://readhostingreview.com Many of my friends told me that they have owned several plates. But I have not owned a single piece of it. I wonder why others are always getting them easily.

As answered, there is only a chance of receiving frags, it is not a guaranteed drop