The Creation Engine is an evolution of the Gamebryo Engine (in that if you grep through it, there still are references to Gamebryo functions / strings).
Likewise Gamebryo was an evolution of NetImmerse (which Morrowind used). I really like the idea of augmenting engines with newer stuff since I find it a shame when proprietary engines (products) drop support and the next game would have to be written using a whole new engine (kinda loses the charms of the original games).
A large company like this can afford to evolve their own unique engines because they have the man power. For a single man or small team, unless the end goal *is* an engine, you probably are not able to invest the 1000s of manhours required to make a featureful engine and a fun game at the same time.
That said, if your game doesn't need "much of an engine", then it might be worth knocking up your own rather than learning a large engine such as UDK, CryEngine or Unity (IMO overkill for 2D and there are simpler and better alternatives that specialize in 2D).