It's a BUSINESS decision.
Businesses frequently spend some money hoping for a payoff. If it doesn't payoff they drop the initiative.
In this case, the decision is money-oriented, but it's not simple.
If Fisher does well, then they have locked in a lower price than if they had waited.
If he doesn't, then they risk little in comparison with the many millions they lose by not listening to the fans. A much, much higher price.
BTW, I pulled these numbers out of the air. 15M is probably high. They probably risked even less.
Look, I hated the Tavon deal with reasoning similar to yours. And I want this FO to change course dramatically.
I just don't think they are planning to retain Fisher, and a few million is not enough of an obstacle to imagine they'll care much about firing him.
It happens all the time to coaches with apparently guaranteed contracts!