My guess is that is what was laying around. Almost all of the vehicles that were to get the LE5 were relative duds:
Chevy HHR
Pontiac Solstice
Saturn Sky
Saturn Ion
Saturn Vue
Pontiac G6
GM probably built inventory based on predicted sales but all of these vehicles had poor sales.
The lone exception is the 2008-2012 Malibu which had strong sales but from 2010-2012 it was only GM vehicle using the LE5 (there may have been in a Chinese Buick as well).
Interestingly the LE9 was only used in the HHR and fleet Malibu's.
Rest assured that the LE5/9 is used due to cost. There are many better engines out there right now (the LE5 dates back to 2005/2006) but I guarantee they all cost more. So would you pay another $2,000-$5,000 for around the same performance?