For those wondering why R-Truth and Carmella were split in the 2019 WWE Draft, it comes down to the USA Network and Corey Graves.
Dave Meltzer reports R-Truth staying on Raw has to do with the WWE 24/7 title and the USA Network. The title was a USA Network idea as a way to get people to stop tuning out for the third and final hour of Raw. While the belt no longer has anything to do with the third hour of Raw, it was a USA Network idea and they didn’t want the title switching shows.
As for Carmella, she moved to SmackDown because of real-life boyfriend Corey Graves. So with USA not wanting their idea moved to SmackDown and Carmella having to go to SmackDown, the two were split.