Ironically, it sounds like the Planet itself was using up mako/Lifestream in a similar way to how the Reactors do. The reason the Planet wanted the Cetra at the Northern Crater to begin with was to "cultivate the land" so that more mako/Lifestream would be there... because there wasn't a lot of mako/Lifestream there after the Planet started fixing itself. To put it how Ilfana did... "the energy that was needed to heal the Planet withered away the land".
If we're just going from the OG, here's what Ifana says about the Northern Crater if you put everything in the order it most likely happens in...
1) "something fell from the sky making a large wound"
2) "the Cetra, heard the cries of the Planet; The first ones to discover the Planet's wound were the Cetra at the Knowlespole"
3) "the Cetra then began a Planet-reading"
4) "thousands of Cetra pulled together, trying to heal the Planet"
5)"the energy that was needed to heal the Planet withered away the land"
6) "the Cetra tried desperately to cultivate the land so as not to diminish the needed energy"
7) "due to the severity of the wound, it (the Planet) was only able to heal itself, over many years"
8) "the Planet tried to persuade the Cetra to leave the Knowlespole"
9) "When the Cetra... were preparing to part with the land they loved... That's when it (Jenova) appeared!"
So it seems that the Cetra were trying to help the Planet make more efficient use of the energy it would take to heal the wound at the North Pole... but they never finished it healing it due to Jenova. So the wound has constantly been a drain on the mako/Lifestream in that area as the Planet keeps trying to fix it.
One of the NPCs in Cosmo Canyon actually goes more into what the Cetra did for the Planet, and it's very interesting how it's put.
A journey to grow trees and plants, produce animals, and to raise Mako energy.
So the idea that the Cetra could control the Lifestream/mako was already established in the OG.
This neatly dovetails with the description given of Ancients in the Crisis Core Keyword section which is even more direct about what the Cetra were capable of.
Ancient
A race who lived on the planet from long ago, and who possessed the ability to speak with the planet. Also known as the ‘Cetra’. The Ancients are said to have opened up Lifestream veins in the land, working to make the planet fertile.
So you have the Cetra being the ones making the Planet more fertile... which seems to be how more mako/Lifestream is made in the long run. Which would have been desperatly needed on the Northern Crater while the Planet was healing the wound their. Seemingly with parts of itself somehow if it's using up mako.