For the same reason that they de-orbited MIR it will eventually outlive it&#x27;s purpose.<p>The modules have a life span, the ISS&#x27;s mission has already been extended beyond it&#x27;s original scope, eventually it will come to a point where you can not maintain it and it actually becomes a risk to the astronauts (we didn&#x27;t had major incidents with the ISS, MIR had a few including a fire, but no major casualties, but after nearly 20 years things can start to break down and a catastrophic failure can very likely result in loss of the entire crew).<p>The ISS is also limited in terms of what you can bring to it, what type of experiments you can run and how can you extend it so in some sense it limits our capabilities.
When something outlives it&#x27;s purpose sometimes it&#x27;s best to discard it because having it and investing resources into it prevents you from expanding and building something new.<p>We&#x27;ll eventually have to build a bigger station that could be used for bigger experiments like micro gravity sustainable agriculture, industrial manufacturing and more. As well as potentially actually simulating gravity and other things.<p>Ideally you&#x27;ll also want a space station quite further away from earth like maybe a 1&#x2F;3rd of the distance to the moon which can be used as a launch platform and a future space dock.<p>Projects like that are going to be very expensive and giving up on the ISS could actually release quite a bit of funding as well as drive the need for a new space station because &quot;well we got the ISS do we really need a new one?&quot; is quite often used as an excuse just like orbiter development was hindered due to the shuttle being in operation for so long.