Does anyone have any idea? I don't. Before the season, Sanchez looked very, very unlikely to perform well at the big-league level. But given that he had an out clause and the Pirates had a banged-up rotation, there was perhaps some justification for giving him a start or two if you liked what you saw from him at the end of spring training.
Now, though, what possible justification can there be? Sanchez has had four starts, and they've gone worse than even his detractors anticipated. He now has 6.35 walks per nine innings, after posting 7.38 walks per nine innings last year. Unless you're, say, early-career Randy Johnson, it's nearly impossible to succeed with numbers like that. Sanchez is 30 years old. The Pirates are 1-3 in games he's started, but his starts have been even more costly than that, because they tax the bullpen to such an obscene degree.
"But everyone's hurt!" you say. Actually, you don't say that, because every single one of you agrees that Sanchez should go, but so far, the Pirates don't. Sanchez has been so bad that the peculiarities of the Pirates' roster just don't matter. Phil Irwin projects to be much better than Sanchez for the rest of the season, according to ZiPS. (UPDATE: I forgot that Irwin is apparently hurt and hasn't pitched in a while.) Kyle Waldrop projects to be better. Pick anyone.
Heck, let's say you're not such a Kyle Waldrop fan. I don't blame you! The Mariners recently claimed Duane Below, who had been in Triple-A for the Tigers. Duane Below and Brian Burres are the same person. And Duane Below is better than Jonathan Sanchez. Fernando Nieve recently cleared waivers. He's really bad! But he's better than Jonathan Sanchez. Finding pitchers who can give you six mediocre innings at least some of the time is not hard, and the Pirates shouldn't have let Sanchez go this far. I'm sure Sanchez will be gone when Francisco Liriano is ready in a couple weeks, but in the meantime, there's no point in wasting a roster spot on him, and certainly not in wasting starts on him.
UPDATE: Sanchez has been suspended for six games for the HBP last night. He is appealing the suspension.