If you grow a pop and build a district or building to employ that pop then your net empire income is reduced because you now need to pay:
- Food to feed the pop, and to feed all the pops paying for all the upkeeps on this list.
- Energy to pay for the district/building upkeep, and the upkeep of all the district/buildings paying for all the upkeeps on this list.
- Strategic Resources to pay for the SR costs of advanced job upgrades, and the upkeep of all the advanced job upgrades paying for all the upkeeps on this list
- Consumer Goods to pay for the extra amenities the pop consumes, and for the pop's living standards, and possibly for the job itself, and all the CG upkeep of all the pops paying for all the upkeeps on this list.
- Minerals to pay for the Consumer Goods, and possibly for the job itself, and for all the CG and job upkeep of all the pops and jobs paying for all the upkeeps on this list.
Civics and origins and Lithoids and Robots and Hive Minds shuffle things around a bit, but overall if you build more mineral production you lose a bit of that to just keeping up with the increased mineral costs of your mineral production, and you reduce your net income of all the other resources at the same time. Every expansion, vertically or horizontally, kicks in a bit of red queen's race just to keep all your plates spinning at the same speed.
But rapidly expanding out to grab more systems doesn't innately reduce your unity or research like it does your energy. Filling out a new research job doesn't lose a little research the way a new food job loses a little food. Unity and Research exist outside this loop. We could solve this by adding unity and research upkeep items throughout the supply chain, but instead we have Empire Size. If you build a new research building and fill it with new pops your empire size goes up, increasing the cost of all your research a bit, which is effectively the same as reducing your research output a bit. If you increase the horizontal
or vertical size of your empire you need to dedicate some of that increase to research and unity just to keep up with your existing effective output - same as everything else.
Alloys are kind of half and half - they have some direct upkeep increases (habitat districts), but the main upkeep reduction is in increased ship costs from needing more ships to defend your territory and to keep your influence coming in. Personally I think they should tack alloy upkeep onto a few things, like outposts and starbases, but that's a conversation for another time.