I have a question. I know governments do [debt rollover](http://www.investopedia.com/terms/r/rollover.asp) from time to time. But, to me it seems logical that governments do this when the interest rate of bonds they have issued in the past is higher than the one they could get now. This way, they pay more expensive debt with cheaper debt. To me this seems like a no-brainer. But is this what they do?

With current QE and low interest rates, are governments doing this? I think they are not. Why?