Half the reason why the Irken Empire began Operation Impending Doom 1 and why Conventia was the 1st planet they ever conquered in the name of their Armada was because they wanted to enslave planets that had surplus amounts of exotic Junkfood. Irken biology is very strange. For whatever reason, Irkens can only ever eat Junkfood which is why Zim's body reacts so negatively to human earth food.
Its also why "The Massive" is used as both a war ship and a gigantic transport ship because its used to lug large cargo containers filled to the brim with donuts which are the All Mighty Tallest favorite Junkfood snack. In fact, half the reason why in the movie why the Armada was just blowing up random planets instead of conquering them is because this is suppose to educate the viewer that Impending Doom 2 is over. Everyone in the entire galaxy, including the Resisty has essentially just dropped any and all pretext of every attempting to outgun the Armada since they've noticed the only thing capable of destroying the Armada are Dib, Gaz and Zim's stupidity and inability to realize that the All Mighty Tallest hate him.
The Resisty believed that without their food supply the Armada would immediately surrender but the problem was most civilizations are absolutely f**king terrified of the Irken Armada and who can blame them. They're using stolen Vort Technology. The Massive, The Mega Doomers, even the SIR bots were all originally built by enslaved Vort Scientists. When you really take the time to process all this, Jhonen actually made a very complex lore driven show when he was namely just trying to make a dark comedy.
