I think prosecution (AC) talked about that at Jake's hearing when he confessed. The amount of time it would take to get through all 4 trials was a key consideration. The family wanted to see justice, but some of them were in failing health. It probably would take at least 5 years to get through all 4 trials. That meant family had to continue showing up for pre-trial and trial hearings month after month, year after year until all of these creeps were convicted.
It probably also meant the trials would eventually need jurors from other counties, due to Pike County's relatively small population. It would be hard to seat 4 consecutive juries in Pike County.
The decisions came after the defense attorneys had a chance to review all the evidence against their clients and realized it would be very difficult, if not impossible to get an acquittal.
GW4's attorneys have worked very hard for the last couple of years to bamboozle some folks into thinking the evidence against the Wagners was weak when, in reality at least 2 defense teams (and probably 3) realized they stood little chance of winning. I say probably 3 because I don't think Billy's attorneys believe he will get acquitted. He has ignored their advice a number of times, on his case. Remember when he made them hassle the judge to have a hearing about letting him out on bail? LOL. They're stuck having to do what he wants. He's a very violent, hostile, poorly educated and delusional defendant. Not sure what the deal is with GW4 and his attorney. I suspect, but won't say.