MACBETH

Elizabeethans felt that the universe had an order to it. When a King is killed, the Elizabethan universe is turned sideways. God's order has been disturbed and "unnatural events" take place with the weather and animals. We see these unatural events take place just before and after Duncan is killed,

The night has been unruly. Where we lay,
Our chimneys were blown down and, as they say,
Lamentings heard i' th' air, strange screams of death,
And prophesying with accents terrible...

So, for Elizabeethan's, it is better to have a hireditary monarch rather than a a "false" monarch. Elizabeethan's believed that even a tyrant King by birth was better than kingly robes, "Upon a dwarfish thief."