Now this is just speculation on my part, but I know he interviewed Schottenheimer first because he was available and Schotty has the ability to interview very well and is affable, in fact, the Jets would have hired him as Head Coach back in 2009, but they felt he did not have enough experience and any Head Coach they interviewed back then the Jets made it a point that he had to keep Schottenheimer as OC.
So Fisher interviews Schotty and obviously came away impressed because they both had a home in Nashville and all that Jazz, then Jackson becomes available. Now fast forward to Tim Walton, Fisher hired Walton, but when Gregg Williams was available Fisher hand to mend fences to bring him back, but he did because he knew Williams was superior to Walton.
I don't know why Fisher did not realize the opportunity with Jackson maybe he felt Jackson would be off & running to be another Head Coach some have posted Fisher did not hire any former Head Coaches on his staff besides Dave McGinnis, but I always wondered why with all the opportunity press people have nobody asked Fisher that question right from the start and why they never asked him why he did not look into hiring a high profile OC that had been at the very minimum an offensive coordinator at the NFL level.
When he was in Tennessee, he hired Les Steckel who had been a Head Coach before then hired Mike Heimerdinger who was on everyone's short list as an OC working under Mike Shanahan in Denver and then Norm Chow, who was a high profile OC in college. A far better track record then with the Rams...Will never understand, but that very reason is why Jeff Fisher is now on the outside looking in and will never ever be a Head Coach at the NFL level unless it's on an interim basis.