People don't use the metaphor literally because it doesn't make sense from a 2nd Law of Thermodynamics perspective. If the Matrix was created by AGI for thr sake of producing energy, it would make no sense at all to keep humans around in pods, because it costs them more energy to keep a human alive than what they get out of the human.

The movie producers realized the problem in later movies and added some mumbojumbo that they were keeping humans around for their neural networks, but that still requires the viewer to take it on faith.