Raising long term rates = central banks reducing their long term debt purchases - they are one of the primary buyers right now, keeping those rates artificially low compared to what free market rates would be. If central banks stopped buying medium/long term debt now, those rates would spike and the economy would choke. They can't do it.

Central banks have a couple of primary mandates - (consumer) price stability ie. keeping inflation in check, and sustainable growth / employment.

As long as the economy is weak and the official CPI figures don't show sustained inflation, they will keep printing (buying debt), in order to protect growth, employment and financial stability. We are getting to the limits of how much you can print without affecting inflation.

They are unable to let longer term rates rise (by stopping or tapering debt purchaces) because the it will negatively impact the fragile economy - unless there is clear indication of sustained inflation, in which case they are mandated to act. This would also be very bad for the economy (inflation/rate rises plus economy stagnating).

The only way out of this mess is for central banks to reduce buying debt very, very slowly and hope the economy doesn't choke and grows out of this. There is no other way.