Earlier quoted context omitted.
They didn't really build their own engine, they bought a re-licensable license to CryEngine, rebranded it to Lumberyard, and started their engine work from that. https://www.businesswire.com/news/home/20160209005740/en/Ama... This sale is speculated to have saved Crytek from bankruptcy, as they were failing to pay their employees at the time. Lucky for Crytek, and Amazon was probably thinking "man, we got a great dea…
I never understood why Amazon rolled another engine. Unreal and Unity are both fantastic. Let your dev teams pick from one of those two and be done with it. Unless your doing something really special theirs no reason to build an engine( if your goal is shipping games )
Unity is pretty much none existent in AAA, it's mostly a mobile engine.