There is no justification for that. All the parties and the actions complained of are in the same state, and if one did file in a different federal court in the same state, defendants would move to have the case transferred to one court. Sometimes that happens even when the cases are all over the US - it happened in the set of 20+ complaints about federal snooping/wiretapping without a warrant.
-- ... otherwise, a judge will combine them into one case --
There are good arguments why he can't do that. In particular, each person has his own personal history and relationship with a biker club (or gang, if you are sympathetic to the control-freak point of view in harmony with the state), making the finding of probable cause unique to each individual.
In addition, damages for each will vary, due to their situations before and after being arrested.
Just remember that Nifong engaged in all the activity claimed about Reyna—
he personally investigated the case (and so lost his immunity as a DA); police in that case lied to get warrants;
Nifong paraded false evidence and statements before the media;
police lied to the grand jury; etc.
And the Duke lacrosse case was gutted by a single judge, who, after combining three different suits, stalled for three years, forbade the taking of depositions or evidence during that time, and then gutted the suits because, according to him,
the civil rights provisions which permit lawsuits of
state officials for violating your civil rights, apply only to black citizens and no one else (ie, not whites, latinos, native americans, pacific islands, etc.)
That’s what one judge with an agenda (defending the state) can do.
And laws, precedents, congressional intent, etc., can be rendered meaningless (unless you want to spend a decade working your case up to the SCOTUS level—assuming then that they would even be willing to hear it).
You’re up against the power of the state, so you have to be
ready for a battle.