Because most of them were stuck with poorly run franchises.
Crennel: Cleveland
Mangini: Jets, then Cleveland
Patricia: Detroit
Judge: Giants (Dave Gettleman era)
McDaniels: C'mon, He went 8-8 with Kyle Orton as his starting QB. The Raiders have been a clusterfuck for pretty much 20 years now
Daboll is TBC
Flores has essentially been blackballed from the league, but he did pretty well in Miami
O'Brien's problem wasn't a bad coach, he was a bad GM, just like his mentor
First line in the article says "if he receives medical clearance"
The only doctor that would clear a football player for full contact less than four months after achilles surgery is Dr. Nick Riviera.