Why should they pay attention to them? There are mostly manipulators.
Exactly.
Economy is irrelevant if money supply can be manipulated. Money drives economy, not the other way around. Because people have an illusion that money's value is constant, it is this illusion give banks power to direct the economy as they wish
Imagine such a scenario: As soon as every merchant heard that FED is going to increase the money supply by 4 fold, they raise the price of everything by 4 times, then QE will not give economy any help at all, or even worse, destroy the USD
The fact that this scenario did not happen is just because people's illusion that fiat money have a constant value, nothing else
The thing is that that illusion only lasts for a relatively small time lapse. In the mean time, those profiting from the freshly printed money can reap in a lot of seigniorage, because they have more money and the prices didn't increase yet. While those at the end of the line will suffer and pay all that seigniorage when prices inevitably will start to rise, because of offer and demand.
If a car costs $ 30 000.- and people now have so much cash that they can afford to buy so many cars that the salesman cannot even provide them as the production doesn't follow, he'll finish by rising the prices (and so will the competition). So nobody is stronger than the market, and in the longer run, printing money will increase prices. Unavoidably. Unless that money flees into specific assets where a bubble is blown (that's in fact nothing else but inflation, but concentrated on a few assets instead of on the whole of economy).
For a while. In the end, it also follows offer and demand.