All (or most) comercial planes also have an amber LED alarm on the caution panel that says PITOT when the PITOT HEAT switch is turned off.

If that alarm was functional and activated before they entered that stall profile, it was, in my opinion, some serious misjudgement by the pilots not to turn the pitot heat on.

But then again, I've only flown a PA-38 on storm conditions, so take this with a huge grain of salt.