He was feeding the Ocampa.
Without him, they had no (replicated) food, and no power for their city after their five year reserve ran out, a reserve that was abnormal and new because Caretaker knew that he was dying.
Remember the pulses connecting the Array to the Ocampan city?
Ocampa (the planet) has no nucleogenic particles. The Nacene did this. In fake made up science, this means that it can not rain on Ocampa. Ever. It's a dead world. No rain means that they can never grow a crop again in the soil naturally. (It also means that you shouldn't have been able to breath. But it's possible that the Kazon were partially teraforming a small area of the planet around their mining operation so that they wouldn't have to wear space suits... Of course this means that they would have been flooding their "region" with water vapour to allow for breathing, and then flushing all that water away beyond their work area after the water particles become stagnant and poisonous.
Of course, all the Ocampa needed was the self sufficiency of their own powersource, and their little underground City could last for a million generations after Caretaker's bought the farm.
Caretaker however preferred that they ran out of food, locked in a box a mile under ground resorting to cannibalism to survive rather than loaning any of them a science text book to learn how to harvest and manipulate duterium from the hydrogen in the planets atmosphere.
Oh.
Lets guess that the shield took up a hundred times more power than keeping the city alive.
They could turn off the shield, if they murdered the kazon.
Or maybe just drive them off world?
After Ocampa turned off the shield, if they were not enslaved or eaten by the kazon, then their 5 year power reserve which the Caretaker left for them, would last for 500 years, not 5.
So yes the Caretaker protected the Ocampa form the ravages the cursed barren wasteland above. A kindly benefactor asking for nothing. I don't think they knew that the Caretaker's people destroyed the planet's biosphere... But the Kazon on the other hand knew him as the asshole in the powerful space station who would kill them if they got too close... Which might explain their complete lack of trust in Janeway acting life a good girl.
Lets be honest.
The only reason that the Caretaker allowed those kazon to stay on the surface of Ocampa is that he must have been sick of all the blood on his hands after he evicted the last ten Kazon Colonies that pitched camp there to mine the VALUABLE cormaline deposits.
They were only there threatening the ocampa because he allowed it.
Caretaker sealed the pulse collectors on the edge of the city with phasers shot from 1/2 a light year away. If he wanted to smash Maje Jabin's camp, it would be smashed and the Kazon on the ground couldn't do jack shit to stop it.
The Ocampa might have been trusting children, but it would have only taken them a couple hours to grow up.
. 
