True repentance is not just being sorry, it is "metanoia", Greek for a complete change of heart, mind and direction!
Many people are always being sorry but never really changing--like King Saul! Poor Saul never learned! He apologised and was sorry many times, but he never repented, he never changed, he never turned and went the other way! Saul would break down and weep before the prophet, and he would break down and weep before David, but he didn't weep because he was repentant, he wept because he was sorry he was being caught! (1Sam.15:24-30) He wept because he was sorry over losing the kingdom, but he didn't really confess and forsake his sin, the evil root beneath the outer show. (Pro.28:13)
Though King David also committed great sins, he had a great repentance--a genuine true change, and therefore God had a great forgiveness for him. He sought God's heart. (Psa.51) He really loved the Lord and he really wanted to glorify God and to please Him! In spite of all his sins and mistakes and blunders, the Lord loved David because he was willing to fight and die for Him!--And David went on to do a job for God in spite of all his sins!