I don't know this is still surprising people! Chip manufacturers/providers have been doing this for decades! Making any form of silicon with multiple separate integral cores means that for cost efficiency, they dedicate the 'unused' space to allow the disabling of certain features or possibly faulty areas.
Binning (separating down to their individual behavioral characteristics-not discarding!) cores on their heat production or frequency tolerance are not the only reasons. Another is one of the pipes through the chip not reaching expectations, they are marked, laser cut ( usually on the tiny board the package is attached to) and shipped as a lower version.
Marked and downgraded versions are usually given a different revision number, but not always!