Space

That's not completely accurate. As the NASA link you shared explains, the normal orbit for the ISS is relatively low at 400km, where atmospheric drag and orbital debris pose a risk. The article agrees that the station could be raised into a graveyard orbit (where it could safely remain for several hundred years; this a standard way to retire space hardware), but this would require more delta V than for a controlled deorbit. In turn, this means a more expensive booster vehicle and mission.

So, the ISS could be safely preserved in high orbit, but no one is willing to pay the price to move it there. This makes me a bit sad, as it means the most expensive and impressive engineering project undertaken by humanity to date will be destroyed.