I think this was actually more of a risk mitigation measure from the prosecution's side if memory serves -- this way if one case fell flat or something happened

I think this was actually more of a risk mitigation measure from the prosecution's side if memory serves -- this way if one case fell flat or something happened (you never know, maybe the judge rules some evidence can't be included or some weird technicality happens that skews the case towards the defendant) they would still have other charges to file to get a second attempt at prosecuting SBF.