Interest rates reflect:
* Demand for debt (the market has little appetite for debt, these days) low interest = no interest from the market
* The risk that the debt won’t be repaid.
* The waning credibility of the rating agencies and bond insurers as means of assessing and mitigating risk.
You left of the important one, which has not been operative since Alan Greenspan sped up the government printing press:
The availability of money
With the collapse of credit due to intertwined cascading defaults, no one has the money to finance these things.
A second question for everyone. 1 in 7 dollars in the US economy goes to health care. With that much money sloshing around, the health care system should be able to finance its own expansion needs. That it cannot is a symptom of how broken the financial system is.