Why does God not accept His servants' act of associating others with Him?

What do the people who associate others with God accept for Him, but deny for themselves?

Verse 71 of Chapter 16

And Allah honored some of you over others with wealth and properties. Then, those who are so honored will by no means hand over their wealth and properties to those (captives of war) whom their right hands possess, so that they may be equal with them in that. Do they then deny the favor of Allah.