Because they would.
Morpheus calls it the “desert of the real”. The phrase is a quote from a book called Simulacra and Simulation which presents ideas that are central to the film (the book is also in the film, but Neo has hollowed it out to conceal contraband, which is a magnificent commentary in itself).
Within the Matrix, every commodity can be provided, including such that have never existed in reality. Mouse speculates that the machines couldn’t figure out how chicken tasted: what if chicken never existed in reality, but were an invention (simulacrum) added to the simulated reality of the Matrix?
Smith (who is, one must remember, an unreliable source) states that the early versions of the Matrix attempted to provide human minds with anything they wanted. There was no reason for the machines to withhold anything from the humans; a paradise or a hellscape would be equally useful from their point of view. How the humans’ nervous systems reacted to the simulation was more important, to avoid “losing crops”.
So is this simulation of Western society ca 2000 CE the best world that the human mind will accept, scaled down from Utopia? Or is it the worst world that humanity can live in without losing their minds?
Meanwhile, outside the Matrix, humans have only the basics. Cold metal, rough textiles, unappetizing food. Something like the Nebuchadnezzar would take a lot of man-hours, power, and industrial tools to produce. Otherwise there is very little in the crew’s environment that is so complex that they couldn’t create for themselves. Their world is bleak, bare, and worn-down. While humans in the Matrix never even have to use their muscles or sensory organs, humans outside it toil. They labour to survive in the desert of the real. What they don’t create is excess or luxury. They tell themselves that the bareness of their existence is a proof of character.
In pain you will bring forth children. In toil you will eat of the ground, by the sweat of your face, bread, until you return to be liquified.
— The Machine God, probably.
Note that many historic civilizations have been toppled by the people of the wastes. Some have claimed that the richer societies became decadent and soft, others that the Mongols, the Vikings, the Almoravids were simply more motivated to band up to raid where they found riches and conquer where they found vulnerability. It makes perfect sense that the outsiders, the humans outside the Matrix, would form a liberation / reformation movement to rid the world of the ungodly machine tyrants.
But everything they know about the past is fragmented and frankly not entirely plausible. What if the outsiders got everything wrong? Maybe there never was a war: humans just decided to escape their problems by creating the Matrix. Maybe humans didn’t even exist before the machines created them as a bionic component. Maybe the whole thing is an experiment. Maybe the current situation is the result of a purge failure: the original outsiders were ejected by mistake or escaped destruction in the liquefaction baths, and managed to survive on the outside and build a new society.
Maybe the outside is just another level of the Matrix, somewhere where malcontents can be exiled to, into a reality that is so comfortless and unforgiving that even they can’t deny its reality.
Maybe there is a Better Place that other Matrix humans can ascend to, where it’s sunny and warm, and everyone is kind to each other, and there is no want or suffering.
But the coarse and dilapidated clothes that the crew uses confirms to us as viewers, and possibly to the characters themselves, that this is reality.
