Space is an incredibly, and unrelentingly, harsh environment to exist in. The station is literally rotting, and it's getting to the point where the things that are breaking aren't really fixable. It's time to ol'yeller it and build something else. This isn't your classic car that can be restored to like-new condition, this is orders of magnitude more complex, and it's an incredible feat of humanity that it's lasted as long as it has.

It's not really a waste of money inasmuch as, the things you put into space are consumables, and you have to replace them before they turn back into dust.

Also, as a complete aside, and unrelated to any of the above, why do you think we left all that hardware in Afghanistan? Don't you think we could have recovered at least almost all of it if we'd wanted to? Because it wasn't like we were really having a ton of hot combat at the time. And, if we could, why didn't we? It certainly wasn't cost, the MIC has the unlimited money cheat turned on so cost isn't a factor in anything really. Couldn't have been public perception, being that it was almost universally viewed as a blunder. When I look at it though, I don't see a blunder, I see a strategic move. Have a look at a map, who's next-door neighbors with Afghanistan? Iran. Does Iran get along with Afghanistan? No. Why don't they get along? Afghanistan is overwhelmingly Sunni Muslim, Iran is overwhelmingly Shia Muslim, and those two groups HATE eachother. Iran, by far, as the better military forces, so, if you want to keep those two countries busy murdering eachother for the foreseeable future, well, you "give" a bunch of semi-modern military hardware to Afghanistan, obviously.

So the real question is how much is that strategic move worth? It's cost somewhere ~6 trillion dollars since 2001 to run military operations in the middle east. We left ~8 billion dollars worth of hardware in Afghanistan, so, if that strategy works, well, it's substantially cheaper than just fighting a hot war with Iran, probably by a few decimal places.