I do know that the 13-14 days of its scheduled life is limited by the duration of sunlight and once the far side of the moon goes dark, the lander will be in temperatures as low as -170° Celsius.
But why is the lander affected by this, given that even other satellites experience eclipses of the Earth, and the Moon, but they still have prolonged lives, and missions like Voyager were alive even when they went extremely far from the Sun?
Orbiting satellites can still have problems with eclipses, from loss of both power and heat but the total time is normally measured in minutes so simply having enough battery power to keep electronics running (and producing heat) and some basic insulation will allow temperature control.
For unlit periods in days heat from nuclear decay is often used, possibly in conjunction with similar electric power sources. These however are complicated to generate the isotopes for and politically problematic to launch.
So a simple and low risk lander design is limited to operation for the period that solar power and heat is available, after which most likely the batteries will suffer irreversible freezing damage.
There are various design options around this, but all of them add cost and complications that may not have been considered worthwhile for this mission.
