He could have tried harder and offered more money. His refusal to invest money in skill positions is showing and he can't draft WR for crap.
Except he did offer more money to Humphries, but Humphries didn't want to break the verbal commitment, and considering the year he had, it was a good thing they didn't sign him.
I believe Amendola wasn't interested in coming back, for whatever reason. He had 60% of his production in 4 games, and was a non-factor in the other 13.
They went after Jared Cook too, but he was concerned about Gronk's status, so he signed with the Saints instead.
They signed AB when everyone thought he was a team cancer, and even chose not to cut him after finding out he was getting sued for sexual assault. It took him threatening an accuser for them to cut him.
Sanu was supposed to be the perfect fit and someone they've been after for years. He was great in his second game, but then he got hurt and has been terrible since.
They tried plenty of things. It just didn't work out.