Changes to cost of servicing a mortgage, seen through interest rate fluctuations, can trigger widespread satisfaction or dissatisfaction towards the government of the day.
When you hold the bond until maturity, irrespective of the interest rate fluctuations, you get the rate the issuer offered when you had purchased the bond.
Lastly, only 6.8 percent of the government's debt carries floating rates, which results in less vulnerability to interest rate fluctuations, which tend to increase the cost of debt.