Pretty sure it's just a matter of wanting to stay true to both Beast Wars Second (which first said the stuff is Earth's life energy) and Neo (which later said the stuff is Unicron's energy), even if that makes little sense.
It feels like the only sensible explanation for how it could be both is if to say that it wasn't always the Earth's energy, but became one with the planet's energy when it was sealed within the Earth, and now the planet's survival has become dependent on the stuff (almost like an addiction).
Though, now with the Primus aspect added to the equation, this kinda fixes something odd that's never been explained. Way back in the first three episodes of The Headmasters, the Matrix was hidden away on Earth to recharge its energy lost during "The Return of Optimus Prime, Part 2". In the final chapter of The Headmasters manga (which was written at the time to tie into the show), this energy the Matrix was recharging with was said to be the lifeforce of Earth. This originally made no sense. But now that we have Angolmois Energy being Primus's energy, and its being sealed within the Earth long before The Headmasters making it also become one with the Earth's energy, means that the Matrix was being recharged by none other than Primus's own energy.
