In A Midsummer Night's Dream, why are Oberon and Titania fighting over an Indian Boy?

Oberon and
Titania, king and queen of the fairies, both want a young Indian boy to be part of their
entourage. Titania wants the child, who is half mortal, half fairy, because she promised his
dead mother, her friend, that she would raise and care for the child. Oberon wants the child so
that Titania won't lavish so much attention on it. As Puck puts it:

And jealous Oberon would have the child

Knight of his train,
to trace the forests wild.

But she perforce withholds the lov¨d
boy,

Crowns him with flowers, and makes him all her joy

Matters come to an impasse. Oberon thinks Titania should obey him
because he is her husband. She believes she should honor her promise to her friend. Their
quarrel affects the weather:

Contagious fogs, which
falling in the land

Have every pelting river made so proud

That they have overborne their continents.

The ox hath
therefore stretched his yoke in vain,

The ploughman lost his sweat, and
the green corn

Hath rotted ere his youth attained a beard.

To gain the child, Oberon is willing to play a trick on a Titania,
putting a love potion in her eyes so that she falls in love with the first creature she sees,
which happens to be Bottom. Bottom is also enchanted, so that he has an ass's head. Titania
eventually capitulates and gives up the boy, so that peace is restored.