The long-term effectiveness of freezing or incinerating bacteria is rooted in how brutal and difficult to withstand such actions are.
Freezing generates ice crystals which, as mdperry points out, "tear and shear the bacterial cells." In theory this could create a selective pressure to survive these temperatures, and indeed akinetes are known to survive the freezing process. However, that is a non-trivial evolutionary step. To fit such a state into the lifespan of a bacteria would call for a substantial mutation. Freezing bacteria for a few hundred million years will likely be sufficient to "teach" them how to survive! Without such a step, it's just not reasonable to survive the abuse.
The same goes for incinerating. Once you get hot enough, the chemistry of organic molecules starts to become a permanent terminal issue. Evolving to beat this is simply really hard. In fact, an autoclave is enough to kill virtually everything, though one strain of Pyrolobus fumarii did survive at 121C in an autoclave.