To Avoid the Cross-Bronx Expressway, for one reason. I-95 sucks in all of it’s incarnations, except perhaps for the 100 mile stretch between DC and Richmond. (LOTS of “Diversions” on that road...Manasses, Fredericksberg, Chancellorsville, Spotsylvania, etc.)
Also, I liked to peel off at RT55 and cruise the mountains of West Virginia for a nice diversion.
A lot of truckers use I-81 because there are very few major metro areas that create gridlock. Basically if you use I-95 from south of Richmond headed north of NYC, you will hit rush hour traffic in at least one of , Richmond, DC, Baltimore, Philly, and NYC. If what I see on the DC beltway is anywhere near normal, this can mean upwards of 3 hours of sub 30MPH on a road designed for 55-70MPH.