Child custody battles

All these years I have heard about couples fighting over child custody after the breakup. But I used to wonder why no one would just let the other take care of children. Why this great desire to raise children, especially given how hard it usually is. This morning I woke up at 3:30 AM, as usual, I saw the news about A-Rod and and his children and a possible explanation came to mind. When they fight over child custody parents are really fighting over (trying to secure) elder care for themselves. It's all just selfish.