Has Julich had anything negative to say (about Sky, not necessarily about doping but just a more two-sided discussion of the organisation), or is it all a very bland "I've doped, and I've seen doped riders, and these guys aren't doped riders" kind of statement that tells us very little in real terms?
I mean, you could argue that a lot of people hung a lot of faith in guys like David Moncoutié because of Gaumont, but Gaumont explicitly announced that his whole team were doping, including several who hadn't been explicitly fingered as dopers, so as he had seemingly nothing to gain from the statements and was actually standing to lose by alienating peers who were now being accused of doping by a teammate, the excluding of Moncoutié and Tombak from the accusations carried a lot more weight in the public eye.
Julich is the man that presided over Froome's miracle transformation, so although he doesn't work for Team Sky anymore, if Froome's transformation that Julich oversaw turned out to be a fraud, it may impact Julich's future job prospects. It could be that he had nothing to say along Gaumont's lines because there was no doping that he saw.
However, having people who have been "in the loop" at Sky and people on the Murdoch payroll saying "Froome's clean. Sky are all clean. It's all super mega clean awesome yea!" is, unfortunately, inherently suspicious in and of itself, even with the résumés of the sources involved. They don't have the 'burning my own bridges by telling the truth' factor that made Gaumont, Hamilton or even Kohl more believable, and as a result it is not surprising if, in view of just how unpalatable the sudden change of Team Sky into all-conquering assassins who destroy world class fields of cycling while breathing through their noses has been in terms of immediate believability in the context of cycling history, people are suspicious of the motives of the people making those assertions to Froome's cleanliness.