It's not quite that easy. Yes, Ed O may be interested, but do we know if Riley has any type of relationship with him? Head coaches typically like to hire coaches they are familiar with and have relationships with. Hiring complete strangers is not something they usually do.
Now, maybe Riley got to know Ed O while Ed O was at USC, but who really knows at this point. I just don't want people to be pissed if Ed O isn't hired.