system
Given the following post, respond as if you're commenting on Reddit:
human
Let's talk about WALL-E's world

So as a citizen of New Earth, I've been assigned to write a report on the missing history of the planet while our forefathers were in space aboard the Axiom and other ships. I know there isn't much for data on this time period, other than the recordings of a few service bots.

Around the year 2100, the Old Earth is declared uninhabitable by BNL and those with the means exit the planet, leaving the WALL-E class robots to clean up the mess. We know that shortly after that (c.a. 2110 ) BNL CEO Shelby Forthright declares the project failed, and orders indefinite hold for all Axiom-class ships.

This is my first big question point. We know that BNL was not concerned with building robust, non-disposable products. So what I believe happened was that most WALL-E units failed, pretty much as designed. The remaining WALL-E that we have with us now was a combination of manufacturing and coding errors that allowed him (if I may anthropomorphize it) to survive until 2805 when the EVE unit discovers the plant. Furthermore, I believe that the original plan by BNL was to get everyone who could afford it onto an Axiom-class ship, and the "cleanup the Earth" project was a simple a ruse. Otherwise, why would you have simple trash compacting robots, when any number of other technologies would have been more effective (up to and including launching all the trash into the Sun.)

Despite all of that, this one WALL-E unit continued to function well beyond his designed lifetime. But the evidence from his cameras shows many things were still wrong with the Earth when EVE landed. We have evidence of massive duststorms, yet all the tracks of the WALL-E units are still visible. Even the glass doors on the BNL ultra-store are still intact. And he can be seen next to large piles of what were called "tires", which should start decomposing after a few decades, if not centuries. So something seems to have prevented the aging of most of the man-made objects on Earth.

Despite all the evidence against BNL, they continued the charade by sending the EVE probes to check for plantlife. But they do it by sending a small robot to scan items individually? Rather than scan for decreasing CO2 levels, temperature changes, precipitation changes, those sorts of signs, they scan for existence of individual plants. Eventually, a probe *does* pick up a plant and bring it all the way back, only to be intercepted by the autopilot via order A113.

So what was BNL's endgame? Assuming anyone onboard the ship had to sell their all their possessions to get onboard, no one had any reason to go back. However, by waiting as long as they did, in the state they did, no one who returned had any knowledge of basic construction, manufacturing, medicine, or any other crucial life skills. Who would fill that gap? BNL. Except that, again, in their incompetence, the ship's computer had gained enough knowledge to direct the people and retask the helper bots to get civilization back off the ground, without BNL's assistance.

Once we get more technologically advanced, there's already talk of going and looking for BNL's bunker, probably on the moon, to see what happened to BNL. My guess is shoddy manufacturing wiped out the lot of them.
gpt
Regarding why the trash didn't break down:  What causes decay?  With the absence of microorganisms, the primary driver is simple oxidation.  Oxidation rate is driven by the concentration of oxygen in the environment, and energy.  Energy, in this case, is usually provided by ultraviolet radiation from the Sun.

There was little oxidation of the tires because the oxygen concentration of the atmosphere was depleted.  Most of it had been reacted into Carbon Dioxide long ago.  At the same time, the ultraviolet radiation that would facilitate oxidation of metals and organic matter is being being absorbed by the CO2, or deflected by airborne particulate matter before reaching the ground.

Essentially, the earth was going through a kind of prolonged nuclear winter.  The surface of the Earth was cool, due to the shielding effect of the high altitude particulate matter.  The atmosphere itself was quite hot, due to the radiation absorbing effects of greenhouse gasses like H2O, CO2, and CH4.  With the air hot, it picked up lots of water from the oceans, and only precipitates near the poles, building up massive ice caps, and glaciers, while depleting the lower latitudes of liquid water.

With little water, oxygen, or heat, to drive the decomposition, plastics will last effectively forever.  The dust storms are mostly high altitude.  Wind speed near the surface is low compared to higher altitude.  

Most of the Waste Allocation Load Lifter units were designed for constant operation.  At the time they were deployed, they were able to collect enough solar energy through the day to fuel 24 hour operation.  When the environment really began to degrade (just after the wealthiest humans had abandoned the planet), the WALL units began to fail from lack of energy.  Later models had gotten a software patch that allowed them to shut down during periods of prolonged low energy.  Those are the ones that lay scattered around the planet.  They didn't fail, they are simply in energy conservation mode.  The problem is that energy conservation mode ranks self-maintenance as low priority, so many eventually failed from neglect.

One point that you should be aware of.  BNL's leadership did not abandon the planet for a moon bunker as you propose.  Like most wealthy industrialists, they went "Galt", and buried themselves in deep subterranean vaults.  Their descendants are still here, living harsh but fair objectivist lives.  From there, they stand eternal vigil, fighting an unending war against the endless communist hordes that threaten to tax them into oblivion.