I was just thinking about that, over the last few days. Like As-Sadr, Hakim came from a "family of martyrs", he had a prestige in that community (Sistani, although very influential and respected, is not from a family of martyrs, and is an Iranian, not an Arab.)
Baqir Hakim outranked As-Sadr, being an Ayatollah, was an entirely different person, with different tactics and future plans. If he was still in Najaf, he would be the dominant force. I always feel melancholy about his death, and I wonder who really was behind it.