Society at the time of Janaka was an agrarian society. Kings led by example. Janaka's name means 'Progenitor' or 'Father'. Sita means 'Furrow'. A plow is used to place the seed in the earth and 'create' the furrow. By plowing the earth, Janaka - the father - was placing the seed into mother Earth. Sita was not born of a human mother, but mother Earth. The story is highly symbolic, although not having a human mother, Sita is still born from the union of a father and mother. See Ramayana 1.66.14-15
Arisen from the earth and not from a mother's womb, she grew up as my daughter. I made a stipulation that (this shall be the means to win this maiden as a gift) this shall be given in marriage only to the prince whose prowess is fully tried. O Eminent ascetic arisen from the earth and reared as my daughter, she has been sought after in marriage by many princes. Ramayana 1.66.14-15