Yes but why keep humans around then, why not just kill them all off? Could be some "Robot Law" injunction, "don't harm humans", but I'd say introducing that would introduce complexity into the setting that detracts from the main themes.

"We're using humans for their computational power" doesn't need much history or exposition as it's a completely practical matter: Suspension of disbelief for minimum investment, a script writer's dream.

[–] Semi_Hemi_Demigod 1 points 8 months ago

Just compare it to adult children putting their elderly parents in a nursing home. Also, based on the Animatrix it seems like it has a lot more to do with keeping humans from fighting back and destroying the earth even more than it does with using them for computing power, since the machines didn't need human brains prior to building The Matrix.