Being mediocre in the NFL is tough.
I think there are three groups of teams in the NFL.
Some teams are at the top of their game, and manage to stay there for long periods of time because they build a culture of winning, have good coaching, and good QB play, and often have a little luck go their way.
Some teams are just plain bad, and lose a lot. But they have the luxury of a few early draft picks, often have some cap space and can lure some free agents, and coaching changes happen. And sometimes that's enough to propel them to another group.
And last is the mediocre group. These are the teams that go 7-9, 8-8, or 9-7 year after year. They don't get the big name draft picks. They overspend in free agency. They don't usually get coaching changes - and when they do new coaches tend to want to rebuild. Luck never quite seems to go their way. And that culture of winning seems nearby but is surprisingly elusive. You'll hear comments like "if only we had x happen in this game, we might have made the playoffs."
The problem is that once you enter the mediocre group its tough to get out. Teams spend decades there wallowing until they get one break that changes their fortunes. It may be for the better, or could be for the worse.
Look around the league. Miami was in the elite group for many years. Now they're in the mediocre group. Its going to take some lucky break to free them. I don't have a clue what that will be, but it has to happen sometime...you hope.