I wonder why do people assume that going forward heatwave intensity will stop before reaching the survivability threshold. It doesn't take too much, you just ne

I wonder why do people assume that going forward heatwave intensity will stop before reaching the survivability threshold. It doesn't take too much, you just need an event where wet-bulb temperature persists over 35 Celsius to have healthy humans start dropping like flies en masse. If they don't have access to cooled premises, that is.