The Creation engine is based on Gamebryo technology... Which in turn is based upon Net Immerse.
It is actually a powerful engine with extremely flexible scripting capabilities and modular middle-ware support.
Often engines are based upon older prior technologies in the gaming industry anyway... For instance, the latest Call of Duty game is still using an engine derived from Quake 3 from all the way back from 1999...
And it makes sense, why scrap something that works when you can build upon it?
Engines like Unreal, Frostbite and so on are also based upon older technologies... And because of such their development pipelines/tools are actually extremely mature... So it makes sense to retain it rather than scrap it unless it is absolutely necessary... Granted if you were to compare the latest version of Unreal with the first version, they wouldn't be comparable, enough changes have taken place over time to assume they are unique variants.
In saying that, the Creation Engine needs a top-to-bottom overhaul as do allot of other game engines.- Will we see that? Who knows. But money talks... I would like Bethesda to go back to pushing the PC like they did with Morrowind and Oblivion rather than bend to the lowest common denominator (Aka. Consoles) like they did with Skyrim... But I digress.
--::{PC Gaming Master Race}::--
