My guess is that is what was laying around. Almost all of the vehicles that were to get the LE5 were relative duds:
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?