Going into 2015 they fired long time head coach Rex Ryan. You can say what you want about Rex, but his teams always over achieved. Rex's biggest flaw wasn't his foot fetish but the huge number of draft busts he collected over the years. When he left the team had little to no talent because of years of failing in the draft. They then hired Mike Maccagnan (which was a huge mistake) as GM and then tried to marry him to Todd Bowles at owner's orders. Bowles is less than average coach, but I don't think he was as bad as his record with the Jets would indicate. He was mostly hampered by Maccagnan who insisted on building the team through free agency. Maccagnan bought a surprise 10-6 2015 season by over paying over the hill free agents. This was a band-aid fix and everyone knew that, but after the season rather than trying to trade away those free agent assets with their newly (slightly) risen value and beginning the inevitable rebuild, Maccagnan doubled down and wasted even more money in free agency. After the Maccagnan/Bowles 3rd season (each season with these two the team got worse) and now, knowing that with one more bad season Bowles at least was gone, they decide to rebuild. They were sitting at 6 and traded away the 6 and 3 2nd round picks to move up three spots to the 3rd. Essentially, they spent a 3rd overall and 3 2nd rounders on Sam Darnold. Which is about an entire season's worth of draft capital to pick up Sam, and unless he became a multi-Super Bowl winning quarterback, the Jets were never going to get 4 players worth out of him.
Add to this that Sam really needed a season or two riding the bench to iron out his serious flaws, and the fact that everyone knew that Bowles as gonna start him right away to save his job and the Jets were probably going to lose enough games to get Bowles fired and then Sam would be on his 2nd head coach and 2nd offensive coordinator in 2 years. I knew that this was a marriage from hell given that Sam would never live up to those picks and that he'd likely never be given a fair chance to.
Sure enough, 2018 ends and 4-12 Jets fire Bowles. But the Jets decide to hold onto Maccagnan (the real villain). Instead of firing the GM, having the new GM find a coach and then proceeding from there, acting (and inexperience) owner Chris Johnsons kept Maccagnan and decided that the new head coach (who he was to pick rather than the GM) would then take on the coaching staff Chris Johnson also picked out. The only person to agree to those terms was Adam Gase who just got ran out of town on a rail from Miami. This hire was universally panned. So Johnson hired Gase as head coach, brought in Gregg Williams as co-head coach/defensive coordinator and thought he could somehow voltron the most passive aggressive offensive mind and the most aggressive defensive mind in the NFL into a great coach.
Needless to say, it didn't work. To make matters worse, Gase didn't even hire a QB coach. Sam hasn't had a QB coach since 2018. Gase gets Maccagnan fired after he over paid for Le'veon Bell in free agency so we go a season with Gase as coach/GM. (Notice how both the GM and head coach could report directly to the owner, creating no line of communication and opening the door to office politics. This will come back into play later in this epic.)
Nobody liked Gase when he came in but at the same time the New York media had to step lightly around him 'cause his staff was quick to ban media personalities from press conferences. Over the last 2 years we went from a team with some pieces but with a few weapons we could be decent to being the worst team in the NFL. Thanks to Gase.
After the Maccagnan fire they hired Joe Douglas, a former scout. Part of that statement linked above was a promise from Chris Johnson to leave the running of the team to the GM rather than trying to continue to Jerry Jones the team into the ground. Now the three biggest problems are gone (Chris Johnson making football decisions, Gase being an idiot, and Maccagnan over paying free agents) the team can go through a proper rebuild.
Oh, and that was Sam Darnold's last game with the team. You don't get to throw 9 tds and 11 ints on what is effectively a contract year and get to keep your job. He's got one year left on his rookie contract and they'll start shopping him around once they've hired a new head coach.
TL;DR: The last 6 years were unprecedentedly bad for the Jets but the biggest problems are now gone.