As mentioned earlier, you get into a situation where you have, for the past 9 mo or so, people who are instituting new programs / philosophies that didn't exist in this org before. One imagine that it is not easy to do... it's not unlike an NFL team switching D coordinators and schemes.
If you sweep all of those people out, you start from scratch; you basically lose a year or so of a new team instituting their philosophy to get back to where you started. Maybe that doesn't seem like much in the grand scheme of things, but the pedigree and track records of Garko, Ribas, Stroop, etc. etc. seem solid and they come from winning pedigrees.
I'm not an expert, but they seem worth keeping around on their record and merit alone, let alone the fact that the place the Tigers find themselves does not fall on them.