It isn't. As Reserve governor Glenn Stevens was at pains to point out, recent figures suggest that "overall [economic] growth is continuing at a moderate pace" notwithstanding a very large decline in investment in new mines and natural gas facilities.
In consequence, employment is increasing and unemployment is, as they say in the financial markets, “flat to down”.
In which case, why is the Reserve cutting interest rates? Good question. Actually, it says more about the trouble other rich countries are having getting their economies moving than it does about ours.
The advanced economies – even the Americans – have still not recovered properly from the Great Recession precipitated by the global financial crisis of 2008.
The long boom that preceded the crisis involved a lot of borrowing by banks, businesses and households, partly to bolster living standards, but also to buy housing, commercial property and other assets.
When, inevitably, the credit-fuelled boom busted and asset prices fell back to earth, a lot of households and businesses were left with assets whose value no longer exceeded their liabilities.
Recessions that arise from such "balance sheet" problems always take a long time to recover from, as households and businesses cut their spending and investing in order to pay off their debts.
That was bad enough. But the difficulties were compounded by governments on both sides of the North Atlantic convincing themselves the problem wasn't excessive private sector borrowing, but government borrowing.
They not merely concluded they should do no further deficit spending, they embarked on the deeply misguided policy of "austerity", in which they tried to cut government spending and raise taxes at a time when the economy was already weak. Unsurprisingly, they made little progress in reducing deficits and debt.
This foolish fashion of forswearing the use of fiscal policy (the budget) to increase public sector demand at a time when private demand was weak threw all the task of restoring the economy's growth onto monetary policy.
From a position in most North Atlantic economies where official interest rates were already quite low, central banks cut their rates almost to zero.
When this did little to boost demand they resorted to the unconventional policy of "quantitative easing" – they bought bonds from banks with money they created with the stroke of a pen.
This was intended to lower long-term bond rates, which it did. But it did more to push up the prices of financial assets than to encourage increased spending in the real economy.
With QE doing little to help, some European central banks have even moved to negative interest rates – actually charging lenders a tiny percentage for borrowing their money.
If this sounds increasingly crazy, it is. But it's the world we and our central bank have to live in.
Historically, monetary policy was designed to keep inflation low. But it's a long time since many countries had to worry about high inflation. These days more of them worry about the opposite problem of "deflation" – continuously falling prices.
We, too, have very low inflation: an underlying rate of 1.5 per cent, compared with the Reserve's target range of 2 to 3 per cent.
This situation has led some to conclude the Reserve's reason for cutting the official rate this week was to help get the economy growing a lot faster, so inflation pressures would build and get the inflation rate back into the target zone.
That would make sense in normal times, but times aren't normal. Nor do I imagine the Reserve thinks a cut of another 0.25 percentage points (and less for people with mortgages) will make much difference to the strength of borrowing and spending.
So why did the Reserve feel it needed to cut by another notch? My guess is it had more to do with trying to reduce upward pressure on the dollar – our exchange rate.
The biggest effect of QE – creating more of a country's currency – has been to put downward pressure on that country's exchange rate. Meaning, of course, upward pressure on other countries' exchange rates – including ours.
Our dollar soared during the resources boom when the world was paying extraordinary prices for our coal and iron ore. It dropped back when commodity prices fell, but its return to more comfortable levels for our export and import-competing industries was impeded particularly by the Americans' resort to QE.
It eventually got down to the low US70¢s and the Reserve regards a lower dollar as a key element, along with low interest rates, in stimulating faster growth in our production of goods and services.
Of late, however, the dollar has drifted back up to about US76¢, which the Reserve regards as a retrograde step.
Get this: contrary to the easy assumption of some people, there's no simple, mechanical relationship between the level of our interest rates (or, strictly, the difference between our rates and those offered by big players such as the Americans) and the level of our exchange rate.
Even so, with no inflation problem in sight – and, indeed, with any fall in expected inflation leading to a rise in our real interest rate – the Reserve decided to err on the safe side by trying to reduce upward pressure on the dollar.
So why did the Reserve cut rates? It's the exchange rate, stupid.