• Hare Krishna,

    The answer we can get from the lord himself:

    gita chapter 4.7

    yadā yadā hi dharmasya
    glānir bhavati bhārata
    abhyutthānam adharmasya
    tadātmānaṁ sṛjāmy aham

    Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion – at that time I descend Myself.

    gita chapter 4.8

    paritrāṇāya sādhūnāṁ
    vināśāya ca duṣkṛtām
    sambhavāmi yuge yuge

    To deliver the pious and to annihilate the miscreants, as well as to reestablish the principles of religion, I Myself appear, millennium after millennium.

    The lord appears in families of Saintly Kings in order to protect the devotees,reestablish dharma and annihilate the criminals.

    Since the Kshatriya kings duty is to protect the general population and make sure justice is kept in the world, the lord many times appears in this varna as son of a King such as lord Rama, or as Maharaja Pritu.
    but also there is another reason:

    Gita chapter 3.21
    Whatever action a great man performs, common men also follows. And whatever standards he sets by exemplary acts, all the world pursues.

    Since the King is the greatest among men (Gita chapter 10: among men i am the monarch) he shows the people in general by his example how they should behave.
    A great example is lord Ram, he is known as Maryada Purushottama, by his perfect example of how a son, brother, husband and King should behave.

    But the lord also appears in other varna's such as lord Chaitanya mahaprabhu who advented in a brahmana family.
    Depending the time or circumstances, the lord descends in a family of devotees in a certain varna, to deal with the situation and simultaneously enact wonderful pastimes with his devotees.

    Hari Bol, Hare Krishna, Jai Gaura Hari.

This reply was deleted.