Mostly because the era haven’t come in time for them.
Appears to me that everyone relies on experience and do what worked before. Unreal Engine 4 seems trying to change that. Imagine how will look Unreal Engine in 2 years? Yeah… I doubt after 2 years people will do their engines anymore…
That’s why I’ve started learning UE4, because it seems as a good investment to learn. Something that will have presence today as well as the future. They just have to keep pushing the limits and everything will be fine.