[yesbabyyes]

As I heard it explained, the original manuscript had the humans kept alive because the Matrix was actually running on the humans' brains as the computing substrate. This both made much more sense than humans as a power source, was more horrific, and a better story.

Apparently this was deemed to hard for the unwashed masses to understand, and we were left with this battery analogy instead.

[wkat4242]

Huh interesting. It makes also much more sense then to have some humans have the ability to change things in the Matrix, considering it was basically running on their brains.

The big question in that case though is why? Why would the AIs keep a simulation of the old world?

[shimman]

Matrix lore is quite cool, if you haven't seen the Animatrix check it out. The Second Renaissance is great world building!

https://www.youtube.com/watch?v=sU8RunvBRZ8 (first part)

To answer your Q tho, this was in one of the sequels I believe, basically the first iterations of the matrix were like "Eden" but humans couldn't adapt to it so they redesigned and iterated it into what you see in the movie. The idea being that if humans weren't busy they'd realize they were enslaved so they had to make a system to keep humans occupied and stimulated enough to be useful.