The court's ruling was based on procedural grounds as Michael Jackson's mother, Katherine Jackson (from whom Joe Jackson is separated), already has a pending wrongful death lawsuit and the law does not favor multiple lawsuits on the same grounds: this legal principle is called the one-action rule.
This case is a good opportunity to review who is entitled to sue for wrongful death in California. The dead person’s surviving spouse, domestic partner, children, issue of deceased children, dependent stepchildren (and dependent minors residing in the household for at least six months), dependent "putative spouses" and their children, and dependent parents can sue for wrongful death. If there are none of these types of relatives/persons, then whoever is entitled to intestate succession may be a proper wrongful death Plaintiff.
It is not clear whether Joe Jackson was dependent on Michael Jackson at the time of Michael Jackson's death: Joe Jackson was not close to Michael Jackson and was not named in Michael Jackson's will. If Joe Jackson cannot prove that he was not financially dependent on Michael Jackson for necessary living expenses such as rent or food, then he probably won't be able to join Katherine Jackson's lawsuit.
