Because the implementation of all the complexity within would be much buggier if they tried to pull it all off from scratch. Also, it would be more expensive.

Because the implementation of all the complexity within would be much buggier if they tried to pull it all off from scratch. Also, it would be more expensive. The official application of ME is, well, about managing the hardware. This means it has to work with lots of different components, including coordination of the resources available. When you think of it, that's pretty much the definition of an OS. Instead of writing their own one, they decided to use one of the ones already available.