They just don't have anyone else to fill the spot. Sosa has clearly been banged up. Guthrie is already on the team, is probably not better (at the plate) and is also supposed to play CF. Everyone else on the 40 is a LHB besides Rojas.
When Pache comes back they could cut Harrison and keep Guthrie. Or when Hall comes back they could just roll with Clemens and go without a righty for while. Ditto if they brought up Cave. But I'm not sure any of those things result in better production from the spot.
And Harrison is also beloved by the front office and the manager so I bet he still makes it to the All-Star break.
In the end I really think they are still going to have to replace Hoskins in some way at the deadline, as per the note below. Harrison was meant to provide at least a little RH pop off the bench, and that's certainly not happening. Turner's been slumping. Bohm has reverse splits. Sosa's brief time with a big bat is already over. They probably need a LF or a 1B. They already have plenty of middle IF/3B guys.
Turner has struggled in general, but particularly against lefties this season. The right-handed hitter entered Fridayâs game batting .182/.260/.318 against them with a .579 OPS. That isnât much worse than how the Phillies have hit lefties as a whole. Their team OBP of .287 against left-handed pitching ranks 29th in baseball.