You've got it all backwards. The dollar should not be manipulated in the ways you are suggesting. In particular the manipulation of rates distorts the credit market. Low rates were the direct cause of the 2000's bubble that led to the 2008 crash. The dollar value is supposed to change in response to the market supply and demand for those dollars. Manipulating it is political. Also there's no decent way to measure the value of a dollar,
Countries have an interest in maintaining a stable economy. Fairly stable unemployment rates. Fairly stable inflation rates. People aren't starving to death, or killing each other over food.
They manipulate the money supply and interest rates to achieve stability in order to avoid revolutions. IMO, its good to avoid revolutions. Lots of people die when there is a revolution, and republics are replaced by tyrannies.
Just because they screw up once in awhile in the rates/money supply in response to political pressure, doesn't mean the whole approach is flawed.
By the way, I'd suggest that the mortgage-backed securities were a lot bigger factor than the interest rates. Banks were lending money with no down payment and minimal credit approval because they could immediately sell those mortgages. The poor-risk mortgages were packaged together and sold as top-grade investments to pension funds, etc. The corrupt rating agencies rated those mortgage-backed securities as high quality investments even though they were full of bad risk loans.
By the way, I'd suggest that the mortgage-backed securities were a lot bigger factor than the interest rates. Banks were lending money with no down payment and minimal credit approval because they could immediately sell those mortgages. The poor-risk mortgages were packaged together and sold as top-grade investments to pension funds, etc. The corrupt rating agencies rated those mortgage-backed securities as high quality investments even though they were full of bad risk loans.