Even if they have the technology to make something useful out of trillions of people's worth of bodily waste, they do not seem remotely willing to use it.
I mean, they actually do have this. At least if we go by the old essential guides in the Legends EU. There's an entire class of recycling droid that are used to reprocess waste on exploration ships so they don't have to carry decades of supplies.
But again, Star Wars is inconsistent and everything is done for style first and substance a distance second.
I think you are using the word "technology" a bit to narrowly here. If magic exists that is the technology in question being advanced. I kind of hate that the word "tech" in modern times seems to refer exclusively to computer stuff.
Especially because language and architecture are also technologies. The thing the 'tech industry' has done is monopolize the idea that an app is the solution to all of life's problems.
CEO - "What do you mean 'the App doesn't magically deliver the food and we have to pay people to do that in the real world'?"
The upper limit is energy though. My understanding is that in the densest places of human civilization the average energy consumption per square meter already exceeds the usable solar energy per square meter, which creates problems if you extrapolate to 'the whole surface of the planet that dense'. If you try to bypass that limit via non-renewables or imports you necessarily warm the planet to the point that you are also going to have to have a plan to export the waste heat or end up cooking your planet's inhabitants.
So just going to do some napkin math on this, and I COULD be wrong.
New York City -
Land Area - 300 square miles - 768,000,000 square meters
Population - 8.3 million - Assume 2000 Calories a day of work works out to - 19920 Megawatt Hours
Electrical Energy Consumption - 11,000 Megawatt Hours per day
- Assume additional energy costs, i.e. internal combustion, are negligible.
- Assume additional organism - i.e. pets and pests, are negligible.
This gives us a total thermal load from the city of New York of about 30,000 Megawatt hours per day or organisms and electrical work.
Solar Output - Average over the year and accounting for day and night, NASA says it's about 342 watts per square meter.
So that's about 8.208 Kilowatt Hours per Square Meter Per Day (342 watts * 24 hours = 8208 watt hours/meter)
768,000,000 meters * 8208 watt hours / meter * 1 Megawatt hour/1,000,000 watt hours = 6.3 million Megawatt Hours . . .
So, I might have gotten my math wrong. But I don't even think its close.
Even assuming our terrible solar conversion ratios, I'm pretty sure our solar power conversion rate is better than 0.5%.
Now, there ARE denser cities than New York. But on average, they aren't THAT much denser. In fact, our tallest cities are statistically quaint little 3-4 story town ships in the Belgian countryside compared to Coruscant or Trantor.
Edit - Apparently, canonically, Trantor has a population of only 40 Billion. Which makes its' mile deep world city a rather strange creation. Coruscant Ironically has the more impressive canonical number in this case, 3 trillion.