Most of the time those who set standards are the ones that do it better "overall". Even if Gears didn't invent the cover system, it's a great game using it really well with everything else working flawlessly and on top of that the game sells. When game companies want to make money and do better than the one that sets standards they go with the one that sells because that's also what they want. If they plan to implement a cover system they'll try to replicate the one from Gears instead of the one from Kill Switch. Same goes for war games they'll go agains't COD instead of Brothers in Arms.
Horde mode might be called another name in Uncharted but the popular one is the one from Gears so Gears is the one setting the standard.
The same will be said about Uncharted when devs want to do more cinematic scenes they'll go agains't Uncharted because it's the one setting the standard,
