Government is about power. It has the power to make laws, collect taxes, and redistribute wealth from citizens to government. 
Government is run by elected officials.
Unelected, unionized government workers have power over elected officials by endorsing candidates with collectivized voting. It is well documented the influence of public unions over politicians.
Powerful unelected government workers with increased control over the government could transform the government into a self-serving organization. 
The trend certainly supports this scenario.