I’ve been using LightningSource since I self-published my first book in early 2012. In the first year, my book sold well and it was consistently listed as ‘available’ on Amazon. Because it was print-on-demand and drop-shipped directly from Ingram/LightningSource when Amazon customers ordered it, it makes sense that it would be listed continuously as Available. Sometimes it would say ‘2 left’ or something, but this seemed like a sales tactic on Amazon’s part because as soon as that number went down to 0 it would say it was Available again.
That changed at some point about 2 years ago. I (and other small publishers) noticed that books were being regularly shown as ‘temporarily out-of-stock’. It’s assumed that this is a tactic by Amazon to essentially “punish” small print-on-demand publishers who are not using Amazon’s CreateSpace. Because being out-of-stock hurts sales, it’s assumed this is a way to strong-arm small publishers to use CreateSpace.