system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the International Space Station considered to be nearing the end of its lifetime? Why can't it be fixed?

I saw the recent news that there were reports of a burning smell on the ISS (which has apparently been resolved), and in the article it described how the ISS was nearing the end of its life. Why can't it be repaired piece by piece akin to the Ship of Theseus?
gpt
1. Degradation is cumulative. So it's not the case that only X pieces fail in a given time period, but rather the number of failures is only going to increase, and it is already prohibitively expensive to send things into space.
2. Not everything can be fixed in space. It is a complex machine and they may simply not have the access or expertise to replace every single part there is.
3. Ultimately, if the end result is you've replaced the entire station, then why not exploit the advance of technology to replace the entire station with something better? Doing this would require diverting resources away from the current station and into a new one.