Democratic governments are an instrument for people to provide services like a social safety net & healthcare to one another and to collectively engage in stuff like fighting climate change and acting collectively on the world stage by cooperation and treaties with other national governments.

If people lose faith in their govenment, they no longer hold it to a high standard, believe in sincerity of government agents, and as a result are less engaged in democratic processes and aren't able to make high quality voting descisions. Sincere do-gooders won't run for office, and instead power-hungry people who can stomach the public distaste for government will run. A spiral of cynicism and distrust also enables actors with antidemocratic agendas like populist parties and strong-man leaders to capture power.