Someone claiming to work for the city posted this a few weeks ago in regards to the lackluster music lineup. Take it for whats its worth. Basically the city's feud with the soda industry over the soda tax might've played a role. VH1, which had been for the last few yrs broadcasting the concert (called the 4th Of July Jam) pulled out this yr. The event's main sponsor was pepsi, and it was pepsi's sponsorship that made it possible for Philly to book higher profile acts (and more expensive), aswell as put on a 1/2hr worth of fireworks (apparently another complaint is the fireworks were short this year.)
Anyway, the guy claimed that either Pepsi pulled it's sponsorship over the soda tax, and vh1 couldn't/wouldn't find another sponsor, or mayor Kenney asked vh1 to find a new sponsor, and they refused. In anycase the person on the Philly subreddit said this was why Philly had such a lame lineup this yr. This was posted about a month ago.