"On purpose" is a multiply faceted thing. It's high enough that it can stay in orbit, but low enough that the Shuttle and other launch vehicles can get to it. That orbit happens to be low enough that stuff does tend to decay fairly rapidly, but I think access was more the driving factor for how high to put it.
Anything in a higher orbit will necessarily cross through the ISS's orbit on their way to decay. So, putting the ISS higher would have been better from a debris perspective, and also would reduce the need for reboosting. But if you can't get to the ISS with the available launch vehicles, that would kind of defeat the whole purpose of the space laboratory.
Greg KO6TH
Patrick Green wrote:
It's my belief that ISS sits in a decaying orbit on purpose so other debris is limited. They constantly have to keep pushing up their orbit to stay in space and not fall back to earth.
73 de KA9SCF