For market participants who own a bond, collect the coupon and hold it to maturity, market volatility is irrelevant; principal and interest are received according to a pre-determined schedule.
But participants who buy and sell bonds before maturity are exposed to many risks, most importantly changes in interest rates. When interest rates increase, the value of existing bonds falls, since new issues pay a higher yield. Likewise, when interest rates decrease, the value of existing bonds rises, since new issues pay a lower yield. This is the fundamental concept of bond market volatility: changes in bond prices are inverse to changes in interest rates. Fluctuating interest rates are part of a country's monetary policy and bond market volatility is a response to expected monetary policy and economic changes.
Economists' views of economic indicators versus actual released data contribute to market volatility. A tight consensus is generally reflected in bond prices and there is little price movement in the market after the release of "in-line" data. If the economic release differs from the consensus view the market usually undergoes rapid price movement as participants interpret the data. Uncertainty (as measured by a wide consensus) generally brings more volatility before and after an economic release. Economic releases vary in importance and impact depending on where the economy is in the business cycle.