If one of the reasons is Gross didn't wanted to play anymore.... Well there are several factors that could lead to him not wanting to play and one of those is his family.
So you proposed that he either just didn't want to play anymore OR he didn't think this team can make it to the Superbowl this year. Do you realize how vague option 1 is? You basically just said there are a million possibilities as to why he retired...OR he doesn't think we can make it to the Superbowl (which seems to be the agenda you're pushing here). Not wanting to play anymore could be attributed to his fear of injury, him wanting to spend time with the family, him not liking Rivera, or hey even...get this...not thinking we can make it to the Superbowl!
Of course if he retired, then he doesn't want to play anymore...that's the only reason for retiring in his case. If you WANT to play and you retire, then you're either injured or no team wants you, neither of which apply to him.