That's because it was all to shady. His family owns the app that was used. They also employed a lead person from the Obama campaign last September as CEO. Remember it was Obama who said if it looked like Bernie would get the nomination he'd had to do something about that. He's extremely rich now and he's not going to allow Bernie to take a piece of his pie. The rest of the people employed are all past Hillary people in design, technology, etc., that worked on her campaign.
There should be a law that person's involved in the development of an app to be used during a presidential campaign can't be related to a candidate.