The tendency of candidates to consciously try to select correct answers undermines whatever predictive validity an instrument may have. Also, many expat candidates have never had a significant immersion experience in an unfamiliar culture. So even if a candidate is trying consciously to select the correct answers, his or her experience base for doing so is woefully incomplete. This further undermines predictive validity. The fact that most expat assessments are self-administered compromises whatever validity they may have.
Personality assessments look at merely one set of variables among many.
The fundamental reason is that, in a highly individualistic culture such as that of the U.S., there is much fascination with individual psychology. Thus, personality measurement is highly developed in the U.S. and personality assessments are readily accepted by the lay public.