There are always multiple variables in play.
First, when you are not a destination job (and GT is certainly not) changing coaches after three years is not going to be attractive to other coaches.
Second, You as an AD have to balance all the money factors, including the contract.
Third, the most important thing from a money standpoint isn't the 'fanbase', its the 'big donors' who pay for big changes. It was the big donors who wanted to change from the previous offensive scheme to the current one and were not going to be willing to put in the money to help unless that change was made. When the big donors decide they are willing to pony up to make a change - that is when the change will happen. They provided the money to support the new staff with more money for coaches, more money for recruiting, etc (that they were not giving to the previous staff).
When the donors who were largely behind getting the current staff hired decide it is time for them to go, that is when it will happen. If they want to pay out the extra money to get rid of the staff early and help pay for a new one, then it will happen. If they don't it won't.