Why on God's green Earth are people still using UE3? Clearly it's not shit as Batman looks fantastic but UE4 has been around now for what, 2 years? More?
A lot of times it's because development starts under one engine and it becomes cost-prohibitive to switch midstream. Also, a lot of times, developers are hesitant to switch to an engine that's still being heavily developed. Epic delivers constant updates and at some point you just have to lock down and work with what you've got. UE3 is supposed to be a known quantity for them, which makes it all the more puzzling why they couldn't have done a better job.