Hooker was screwed, but your title statement isn't factually accurate. Kerryon Johnson was the Offensive player of the year for the SEC in 2017 and wasn't invited. The year before that was the last QB, Jalen Hurts, who was the Offensive player of the year not invited to the Heisman.
Now what is truly baffling though is that Hooker, as the SEC Offensuve Player of the year was not only was bypassed for the Heisman, but another QB in the SEC was invited, Stetson Bennett. That, I'm not sure has ever happened.