Maybe Blake feels like extending TMac will give him more rope with the owners. "Well, we have to pay this guy if we fire him or not, so we might as well keep them both."
Dude has shown he can't make adjustments in the playoffs. What's the harm in waiting until the end of the season? If it plays out like they last couple of years and you want to rehire him for some stupid reason, you have the leverage to lower his salary. If he wants to bail, so be it. If he coaches them to a championship, great. You will pay more to retain him, but at least it's justified.