Thus Absalom did to all of Israel who came to the king for judgment. So Absalom stole the hearts of the men of Israel.
2 Samuel 15:6
Absalom excelled at conspiratorial passive aggression. He used this warped skill set to maximum effectiveness in order to get his own justice and kill his own brother in a family tragedy in the king's house. He used it to slowly turn the political tide his direction when he had a strained relationship with his father king David. This was aggravated by his father's own passivity and aided by Absalom's own natural charm, stunning good looks, and amicable personality.
Of course, the reason this happened had a divine purpose. God warned David pain was coming. God judged David with consequences after his sin with Bathsheba and the murder and subsequent cover-up of Uriah her husband. God told the king that a sword would not depart from David's house. And it seems that Absalom was the strongest and dearest to swing that sword of judgment as God promised. It cut deeply into David's heart.
Every line of the tale of Absalom's revolt and the civil war in David's own family is telling us to be warned: Sin has painful consequences. God judges sin. Our sin brings us misery. We need the mercy of God and the grace of God as we live among those consequences.