A question in their minds is whether candidates have the tenacity to stick through ups and downs of a company. This happens very frequently and I guess the employers are trying to gauge whether people will up and leave the moment things get difficult.
it may merit some nuanced explanation when such a question comes up.
When "things get difficult" is a catch-all of subjective nonsense and to paint it in a more charitable light is intellectually dishonest.
Whenever "things get difficult"—whatever that means—you can count on the recruiter not being around and is why their opinion does not count for much. Often companies will let referrals skip introductory recruiter call entirely. Recruiters are invaluable to form cohesive teams in a startup, but they're glorified secretaries for hiring managers at a large corporation.
Anyone that believes they can deduce a person's commitment to some abstract mission statement based on a few historical facts and a couple hours of interviews is not a serious thinker. It denies the genius 1000x engineer whom quit to move across the country and take care of a sick family member or two. And it denies people with the self-respect to say no to unethical demands by executives. This might be a minority of applicants, but claiming to hire the best necessarily means reducing the type II error rate to zero.