This has been a popular question recently -- why Giancarlo Stanton hasn't been given DL status by Yahoo!. I am happy to answer this for you, and for others who are wondering the same thing.
It all comes down to the fact that the Marlins haven't officially placed Stanton on the DL yet. For a player to be eligible for DL status in Yahoo! Fantasy Baseball, they must be on the official MLB Disabled List.
The Marlins are waiting until just before game time Friday, when they will activate Emilio Bonifacio from the DL to take Stanton's spot on the 25-man active roster. Stanton will officially be placed on the DL at that time -- most likely, retroactively to the date he originally was injured.
Bonificio was playing in rehab-assignment games during the All-Star break, which explains why the Marlins didn't make the move until Friday -- to allow him to remain in the minors to play these additional rehab games.
I know for Stanton owners such as yourself, it's a bit confusing to know that a player is injured -- and in Stanton's case, already had surgery -- but isn't eligible for a Fantasy DL spot.
However, it is entirely up to the real-life MLB team to place the player on the DL, which then makes him eligible for the Fantasy DL.
I hope this answered your question for you. Good luck the rest of the season!