Who makes these decisions

Bill Callahan was hired by the New York Jets to be the Assistant Head coach, as well as run the Offense. Honestly who makes these decisions. I mean was it the prolific offensive outburst by Nebraska last season. Leading the Cornhuskers he managed to take the program to its only losing seasons in 45 years. He didn’t set that distinction in his prior stint as the Oakland Raiders coach, instead he took over a succesfull team from Jon Gruden who promptly pounded him in the superbowl. Callahan then finished up in Oakland by posting a 4-12 record and drawing the criticism of almost every veteran in his locker room.
What, in that resume, had you clamoring for him. I mean honestly, find a college coordinator who wants a shot, find a kid who is good at Madden. Something, anything just don’t recycle empty garbage.