> My question is why Open Connect Appliance wasn't even in their network in the first place?

By having Open Connect Appliance network gives up ability to traffic engineer Netflix, which may decrease the leverage the network has with its peers or its transit providers.

Fundamentally, unless someone must peer with you (settlement or settlement free) and must peer with you on your terms ( locations, types of connections, etc ) you always want traffic that you and only you can control.