The reason behind "demoting" Voit is likely due to the fact that New Jersey is closer than Pennsylvania to the Bronx, which is where the Yankees will be back to this weekend when the Oakland A's come to town.
Manager Aaron Boone noted earlier last week that if all goes well for Voit, then he could rejoin the team at some point within the week. That could mean this weekend, so worth keeping an eye on there.
Voit is going through his second rehab assignment of the season thus far after suffering an oblique strain right after coming off the IL following meniscus surgery.
In 12 games with the Yanks this season, Voit was slashing .182/.280/.250 with one homer in his eight hits. He obviously wants to turn that around, and the Yanks could certainly use that from the reigning MLB home run leader.