Because of IP laws, I believe. Even China can't rip Apple's trackpad tech and copy it because they _really_ like having iPhones made and sold in China... can't rock that boat. But if the latter wasn't true, you'd have 500 brands with an Apple-like or better trackpad.
I don't know if I believe that. Nobody seems to be reaching for absolute top shelf quality anymore. You have Apple, then you have every other computer maker battling it out to try to win the "low cost plastic junk" market. A few of them have a "premium" tier which itself is still comparatively low-cost and sub-par.