Translation:A person has on average one hundred thousand hairs.
In fact, there is a simple answer to your initial "why": because this variant is not in the database. It is not there either because it just has not been added (and should be reported and added then) or because it is incorrect.
As to your translation, I'm not sure if it is valid to translate "en moyenne" with "approximately". "On average" and "approximately" are close but different things. Also, I'm not sure about using "own" for "hairs" in English, a simple "have" seems better to me, but I'm not a native speaker.