There's a simple reason for this: In order to set a record like that you have to be good enough to hang around for a long time.
In Fisher's case, I suspect he's lost a lot of games just because he's usually been coaching teams that aren't very talented. I would just ask how many really disappointing seasons he has had, where he was coaching a very talented team but failed to have them play up to their high expectations.
Fisher’s lifetime is barely above .500. Dan Reeves has a better record than that. The Rams gave him five years, and a LOT of control and draft picks to shape the team as he saw fit. Five years later, the team is as bad or worse than when he got it. The Titans also failed to improve in his last years.
In the game before he got fired, it was clear that he lost the players themselves.