It was certainly unexpected. But pretty much every fan base expects that when a coach is fired, Gruden or Saban is walking through the door. In 99.9% of cases, its patently absurd.
There are a number of coaches who were available at the time, Riley, Frost, McElwain, Hudspeth, etc. After 7 years of Bo, chief concern among the fan base and administration was an experienced D1 coach, not to take fliers on unproven coordinators. Unproven in that, they had never even once put a staff together or led a whole program, not that they hadn't necessarily been a part of a lot of winning for someone elses program.
The number of proven Head Coaches with one or more conference titles and possibly even National Titles who were available in December 2014 was zero. So now its a matter of what aspects do you compromise on, for Riley it was the fact that he doesn't have a stellar record, but he was at a poor football school.
Keep in mind that every time there's an opening, there's not always a stellar coach available. In 2008, we arguably hired the best coach of the bunch, and he ended up being Bo Pelini. Its also the reason UT ended up with Strong, a great name, but not a Saban-esque resume. And UT has no scruples and an unlimited budget.