Presumably Amazon ended the program because it was not profitable and had no prospect of becoming profitable soon. If it was already fully automated and only employed humans for QC and/or AI training purposes, then it's hard to see why they would have killed it.
I suppose there is meant to be a tipping point where the humans should be able to step back after the AI has learnt enough from watching them. Perhaps they were struggling to reach that point and the failure rate was remaining stubbornly high.
Outsourcing to India/Mechanical Turk is always going to be cheaper than creating a sophisticated AI model. I could see them dropping it if the "learning" had started to stall.
This whole thing seemed like a branding exercise anyway. Like how Apple stores are in every major city despite relatively few people buying their products in-store.
