The interest paid on bonds is directly related to the risk of holding the bond (or, the perceived risk). A high interest rate (which the government pays) is the only way the government can get people to buy its bonds, because it's considered a high risk.
It pretty much means that, people aren't expecting Greece to be able to pay back its debt in 2 years. Which is really bad, normally, short term bonds have lower rates (because the risk is lower)...but now, even at 2-years, people see huge risk.
People want 75% interest on, what is essentially, a 2 year loan. Compare that to other parts of the world where you're taking 3% on 20 years....20 years is a long time, anything can happen, but even over such a huge difference in time scale, greece is a much, much, higher risk.