I think this was a great hire for a couple reasons. Ok maybe "great" isn't the word, but Marrone is underrated. He took a Syracuse team that had a near 10 year winning season drought, back to a title and a winning record. He gave the bills their first winning record in 10 seasons, and then quit. People like to look at the 15-17 record and that he left and think he sucked and got fired. Not the case.
Not saying he's amazing, but he's a solid hire for the above reasons, and also that they get to anchor him with Coughlin.
Perhaps the main reason is that with LA, SF, Denver, etc jobs on the market, Jacksonville has to be one of, if not the least desirable coaching jobs to go to. Constant failure there, small fan base, not necessarily a TON to work with, and a bad season. They weren't gonna get one of the big names, and if they waited too long, they could have lost Marrone too as there are more jobs than good candidates. Good of them to shore him up when they did.