Normalcy bias
Etymology
From normalcy, "the state of being normal." The concept comes from disaster and emergency research, which repeatedly finds that during fires, floods, and evacuations many people delay, disbelieve the warning, or carry on as usual — a lag sometimes called the "normalcy" or "incredulity" response.
noun · /NOR-mul-see BY-us/
The tendency to underestimate a looming threat and assume things will keep working as they always have.
What it names
Why people finish their coffee as the alarm blares — the mind treats "it’s always been fine" as proof it will stay fine.
Example
Normalcy bias kept half the office at their desks during the drill, sure the sirens were just a glitch.
Related idea
Optimism bias assumes good outcomes for you specifically; normalcy bias assumes continuity — that whatever has held will simply keep holding.