'Idhuvum Kadandhu Pogum "
Even this challenging situation would ease
But the main reason is that permanency will create vested interests. Election commission has to conduct elections in an unbiased way. If the election staff are permanent employees, then they will naturally become government employees and will not be able to be free and fair.
Even in the case of government employees and bank staff, there is periodical and regular transfer to prevent developing vested interest at a place.
Now when the personnel are deputed from various sources, they do not have any particular permanent bias toward the election department except for conducting the given task during the elections as per rules and guidelines in force. Before or after the elections they are not accountable or connected to the candidates . So they can be free and fair for the task.