There are many reasons, but one key reason is solar radiation. The current orbit of the ISS means that is mostly protected from harmful radiation by Earth's magnetic field. If you moved it away from Earth, you would not have that protection and the station would become very dangerous.

Another reason is resupply. The station can only run for a few months or a year without resupply, and the further you move it away the more difficult and expensive resupply becomes.

There are a host of other reasons, but they all stem from the fact that the ISS was engineered to always be close to Earth, and the space environment elsewhere is sufficiently different that the ISS basically can't work in a dramatically different orbit.

Thanks - those make sense. I wonder if there is any opportunity to keep it in use or relevant. We spent $140 billion putting it up there, so if its not viable to spend 2% of that per year keeping it going then I understand the need to deorbit.

Yeah, we can keep B-52s flying for 50 years with insane numbers of launch-land cycles, I'm pretty sure the ISS can fly for a very long time. SpaceX can already resupply it. I don't see why they wouldn't take it over.

B52s can be completely disassembled in a shirt sleeves environment and we've barely explored on orbit construction. The ISS can't be stripped down so far which is actually causing an issue with bacterial growth in places that can be reached on orbit to be cleaned. At a certain point things that are hard/impossible to reach will reach the end of their lifespan and the inhabitants are in too much danger.

https://www.rt.com/news/iss-bacteria-mir-mutation-765/

Unlike the ISS, B-52 airframes get pulled in to base for regular inspections, teardowns, period refittings/reftrofittings, et cetera.

We can hardly park the ISS in a NASA hangar, refurbish it, and send it back on its way.

Well, for one thing, where do they get the hundreds of millions of dollars it would cost to "take it over"?

How about moving it further up, but making the station completely unmanned, run by robots. They don't even have to be autonomuous, due to the low distance they can be remote-controlled -- fewer resources needed to keep in orbit, fewer resources needed because there aren't any humans. Plus the main inhabitants don't have issues with the vacuum of space, so many experiments could be parked 'outside', maybe on those lattice structures.

Used where and for what? The international space station was originally intended as a low earth orbit base for human space activity, then gradually morphed into a low-gravity laboratory.

Drop it on the moon if nobody wants it. Could be a Theme Park when we settle.

The space station can't hold itself together on the moon, it is not built for 1/6g; you might be able to position it in lunar orbit, but that would be quite expensive; higher orbits would preserve the station just as well at much lower cost, but the station would be an unsafe derelict in a few years.

Would it really be all that expensive though. We are going to have to send tons of mass out there eventually. Is there anything fundamentally different about a lunar orbit that would make such a base not as useful. I understand it was not designed to experience large acceleration forces but could we not use this as an opportunity to test ion drives and/or other low impulse drive mechanism? Slowly inch it towards a linear orbit? Then send astronauts to meet it in orbit with a next gen reusable lunar lander? On a SpaceX heavy and or SLS?

I wasn't really serious but I guess it was too well hidden when I look at the votes ;)

Nice idea. But, just to play with the numbers, it would require tons of fuel and, unless ura thinks of a debris field instead of a park, we must break and descent it there.

I suppose that whould cost a lot more than 140 billions.

some modules might be re-purposed for a Nautilus X, https://en.wikipedia.org/wiki/Nautilus-X

Are you still driving that 1992 Satern? Why not?