As an interviewer or hiring manager why wouldn't you ask about it?
Maybe they were sick, maybe they were pregnant, maybe they were looking after a dying relative, maybe they were backpacking across South America, maybe they were sitting at home watching every episode of Star Trek, what people do in their own time is a private matter.
I suspect that among the hundreds of discarded resumes for a particular role was a candidate who actually believes in the company, would have been fully engaged with the work, and made a serious positive impact on the company’s success.