While many accidents do involve fault, there are scenarios where an accident can occur without anyone being legally at fault (mechanical failure, natural disasters). It does excludes malicious intent though. in the specific context of commercial motor vehicle regulations in the US, the term "accident" is defined in the Electronic Code of Federal Regulations (e-CFR) under 49 CFR § 390.5

Colloquially, accidents are random events without intention or fault.

That's why there's a push to use neutral terms like "crash" that don't imply that the "accident" was just a random accidental mistake.

And fault is often a bit of a misnomer. Many crashes are the result of bad design, but the courts would never say "this pedestrian fatality here is 40% the fault of whichever insane engineer put the library parking lot across a 4-lane road from the library but refused to put a crosswalk there or implement any sort of traffic calming because that would inconvenience drivers".