One possible way to look at it: With a planet already at a certain state of development, there's a lot of interconnected systems and rules that have to be taken into account... but with a low quality planet, it's a blank slate. You want a continent here? No problem, there isn't a trans-atlantic current to mess up, do with this ground as you will!
Those systems existed long before humans walked the earth. Uncolonized planets aren't blank slates, their morphology is well defined - pop or no pop. Granted, humans have somewhat changed the earth's environment, but not (yet) at a basic level.
the lower the quality planet the less population it can support, it might be able to produce enough food, however, the planet just can't grow any larger in population, however, you can transport other new colonists in and it will stay at that number as long as it's less than the planet cap on food. if you upgrade the planet to a higher quality then it will allow the planet to grow to a higher pop.
Which makes no sense at all. Low PQ = low pop, fine. The rest is bogus. You have the space, you have the food. What else do you need? You can have more pop than the max allowed by PQ, but not by breeding? A celibacy pact?
Or is it that only the initial settlers actually *pay* their taxes? Heh.
