Batteries or Generators don’t just let you cook and stay warm when the power is out but do everything else such as keep food cold as well.
An 8kW generator suitable for occasional use is only ~1,000$. A Powerwall 3 does 11kW continuous and peaks at 30kW for transitory loads like starting heavy equipment.
The most convenient solution where a generator automatically kicks in during a power outage requires an electrician and extra equipment, but there’s also real tradeoffs to having gas lines going to your home.
I think part of the problem with whole home backups is that they tend to be sized to a maximum load that is unusual or could be avoided with some effort. And that providing a backup for the essentials you actually need is relatively cheap and uncomplicated if you make some modest sacrifices.