The excuse would go as follow: when you have little in your planet, you have to use these resources very carefully. On the other hand, if you have more minerals on your planet than you know what to do with, you have no incentive to spare them, and so you will likely waste some of them.
It should be possible to mod the resource generation directly on the monsters (either on the hull, or on the components themselves; it should work on the hull, but I haven't tested it). The problem may be with balance however, as it may make the monsters too powerful. I am by no means an expert on the Space Monsters though, so don't quote me on that. It can certainly be done, but do you want to?
