Because they exist only in the security mode. Private sector jobs, especially good/ excellent/fabulous private sector jobs, are infinitely better than crappy government jobs. People in private sector jobs really have to produce and prove their mettle. The keyword for private jobs is WORK and MERIT. The private sector reward their employees more than the public sector where everything is based upon passing some inane civil service test.
Government jobs are somewhat reminiscent of the communist government. Even if a person bust his/her assets working hard, he/she will not get promoted unless he/she passes a test. This means that a mediocre employee can pass a test and be promoted. Private industry encourages initiative and excellence while the government/public sector only encourages bootlicking, obedience, and mediocrity. Initiative is not rewarded as much, if at all, in the public sector.
However, the reason why some people maintain that government jobs are permanent jobs is because one cannot be fired from them unless he/she commits an egregious act and have time/attendance issues. A government worker can be the most incompetent and he/she remains working until he/she retires. It is extremely difficult to fire an incompetent government employee because there are strong unions to defend the employee. Also many supervisors in the public sector do not wish to go through the paperwork that could led to either disciplining or firing the employee. People who work in the public sector know this and know that they can get away with stuff which would never be permitted in the private sector.
There are those in the security mode who believe that private employment is highly precarious because they believe that in private jobs, an employee can get fired for any reason especially in an at will employment state. They believe that private companies do not provide the level of job security that government jobs provide. They further rationalize that although government jobs pay less than jobs in the private sector, the level of job security is far better.