Bond prices are driven by US treasuries and to a lessor extent by high yield default rates.  Treasuries have stayed low because of geopolitical uncertainty, savings as a means to offset trade imbalances, enormous global government pension schemes and other savers.  Supply and demand drive prices in bonds in the regular course with rapid spikes down in rates when really bad events occur.  On the default side, Greece, Italy, Ireland and high yield have all stayed solvent.  Rollovers of debt have gone well and the market continues to chug along.

The demand for government bonds is not going away.  With the reduction in CDO products and other levered means to own debt the credit market, feedback loops have lessened too.

All to say, inflation needs to come roaring back for bonds yeilds to move upwards in a material way.  There are no central bank or economist warning about rapid inflation.  Mean reversion is not as strong a force as most think in markets.  Momentum is more powerful force.