It's truly mind boggling how they've managed to be so bad.
Like most things, it starts with the top down. Their owner is incompetent (lol @ UT), and he routinely fires coaches after 1-2 seasons. No matter what you're doing or how bad the coaching is, firing 4 consecutive coaches after 2 seasons max will lead you to 0-16 over and over again. If they had trusted the process they've likely still got this off-season's HC darling, Pat Schumer, running a pretty fun offense with a bunch of rookie contracts.
They've also gotten REALLY unlucky with all those 1st picks. Outside of their #1 this past year, they've largely all been busts in the last 3-4 cycles. Even when they've done the correct thing and traded down for more assets or picks, the guys chosen with their former pick end up being MVP caliber QB's. The only moment of brilliance they've had in the draft, ironically, is taking Trent Richardson and then waxing the Colts by trading him.
I think Haslem finally said "yeah, ok, I shouldn't fire coaches after 1 or 2 seasons anymore because my team is garbage" and that's why I thought it was smart not to fire Hue Jackson, even though he's by far the worst NFL coach by a wide margin. The Jags just proved you can have stability while employing technically the worst NFL coach in history of the league while shoring up your roster and then take a very, very untalented offense within a few yards of the Super Bowl. They're probably going to win a few games this year against some teams in the middle, but then I think they're probably on a path to being pretty solid in 2-3 years. The signs are there, although losing the best LT of his generation this off season isn't going to help.
EDIT: Important to remember that they're technically an expansion team that debuted right around the same time as the Texans, and the Texans haven't been much better during the same stretch.