In fact, only three books of the Hebrew Scriptures, 1 Chronicles, Job, and Zechariah, mention Satan, which means “Resister.” Why was little said about our enemy prior to the arrival of the Messiah?
3 Apparently, Jehovah did not want to give Satan undue prominence by devoting large portions of the Hebrew Scriptures to discussing him and his activity. Jehovah’s primary purpose for inspiring that section of the Scriptures was to identify the Messiah and lead God’s people to him.
Or it could be that Satan wasn't an important part of Jewish beliefs at the time. Perhaps the bible isn't this coherent book with a singular theme at all. Instead of just making up an explanation that fits the doctrine, more research should be done. Are these simplistic explanations supposed to help people with doubts? I'm not sure why they would even want to point this out?