Malbim: David never seized kingship when he was anointed, or in Sha'ul's lifetime, even when he had the opportunity to kill him. Also when Sha'ul died, David killed the one who told him, and lamented over Sha'ul. He was reluctant to establish himself as king; perhaps Sha'ul's son should be king ¹ , and David's time did not come yet. If so, it was dangerous to return! David attribute over Sha'ul was that he cast his worries on (i.e. asked) Hashem.