I believe some of them came here for $$$ (Marty, Spurrier, Shanny) and because danny boy lied to them about letting them having control or full control.
About Marty : Snyder sells Schottenheimer on 'Skins
" Certain things, like Schottenheimer said he could never work for an owner like Daniel Snyder. In fact, when Snyder first fired Norv Turner, I asked Schottenheimer privately whether he would ever allow himself to be a candidate. Schottenheimer told me to not even consider it and to focus on other candidates. He later basically shared the same thoughts with our ESPN audiences on "NFL 2Night."
He "bought" Spurrier, making him the highest paid coach. Him and Shanny were supposed to have full control while danny boy never let them pick their QB and some FAs. Steve Spurrier reveals secret about his time with Redskins