Heatwave in SE Australia

[ZenGum]

Ducks and Kingswood have checked in, Alphajerk hasn't lately, but he's an occasional poster anyway.

TW, there are many factors and each case has different combinations of them. You've already listed most of the factors.

These fires have come at the end of a drought, everthing is tinder-dry. The record-breaking heatwave primed everything. Strong hot dry winds drove the fires like a bellows until the fires got big enough to create their own weather and become self-sustaining, creating even stronger winds and even lightning. The direct radiant heat becomes so intense that volatile chemicals are boiled out of pine and eucalyptus trees in advance of the fire front and the air itself can become explosive. Hell, the trees can explode. The fire front moves at varying speeds but uphill and down wind 60kph is not unknown. The upwinds throw burning embers several kilometers away from the main fire.The fires are so intense that survival is very unlikely - you need some kind of concrete bunker or similar. Even brick homes get blasted to the ground - bricks shatter with the sudden burst of heat.
The number and size of the fires (30+ fires, burning on hundreds of kilometers of fronts with a total area already in the 250,000+ hectare range) means that firefighting resources are stretched thin.

Human factors are also big. People have settled into hills and gullies with poor access roads, built homes amongst trees, and allowed trees to get too close to houses and drop leaves and twigs all over them. Many of these towns are heavily treed throughout (and so have no refuge within them) and have only two roads out, one each direction, which are easily cut.
Many people were not adequately prepared to fight - no independent water supply or pump, wrong clothing, no plan, not enough people, etc. Many whose plan was to leave did indeed not leave in time - it is not yet clear how much of that was through poor warnings, or complacency. Others planned to stay and fight and got overwhelmed by a fire much fiercer than they were prepared for. Worst is those who changed from staying to fleeing at the last minute. One fallen tree blocking a road leads to a four car pile up with no escape.
Some people may have not heeded warnings on the first day, but I'll bet they are now.

These are the main factors which appear in various combinations. A Royal Commission (major judicial investigation) has been announced which should answer your questions properly (and damn good questions they are) but it will take a long time.

In short, this was not a regular bushfire, but a firestorm, a huge intense fire, moving very fast through difficult country full of ill-prepared humans.