https://www.amazon.com/Man-Corn-Cannibalism-Prehistoric-Southwest/dp/0874809681
Man Corn: Cannibalism and Violence in the Prehistoric American Southwest
and the video of the PBS documentary:
https://www.youtube.com/watch?v=VWbWPgjJ7W0
Since this evidence came as neaderthals were disappearing from the scene, and knowing that homo sapiens already practiced canibalism—its not a big stretch to figure that
these neanderthals were eaten by humans.
The reason would be pretty simple. The homosapiens would do it for the same reason that humans have more frequently practiced cannibalism from the beginning of time—not for survival — but rather to gain energy/power/mana/juju of the being they had just fought to the death with.
Since the Neanderthals would be such a deadly opponent—its not a big stretch to figure that they were hunted ritually to gain their power.