Joke of the Day, as told by Joe Palca

During some free time away from a scientific meeting in LA, a PI and her two graduate students are walking along the beach.  They stumble upon a lamp in the sand, and one of the students picks it up and rubs it.  Out pops a genie, who says, “Since I don’t know which one of you found me, I’ll give each of you a wish.”
The first graduate student says, “I wish that you send me skiing in the Alps, with fresh powder, beautiful mountains, and a snifter of brandy when I’m tired."
The genie grants the wish and the student disappears in a poof of air and sand.
The second graduate student steps forward and says, “I wish to be scuba diving in Bermuda, and I want good visibility, amazing marine life, and a nice mai tai afterwards.”
He also disappears.
The genie then turns to the PI and asks for her wish.
"I want them both back in lab after lunch.”

As a graduate student whose absence from her lab has been sorely felt over the last few days, I appreciate the sentiment of the joke.  But what I can’t figure out is why, WHY, didn’t they wish for their PhDs?