The NFL confirmed to PFT that Simon was not fined for the punch.
The league office doesn’t offer explanations when players aren’t fined, but this is a surprise: The officials were right on top of it and ejected Simon immediately, and ordinarily that would result in a fine as well. And although players aren’t paid their base salaries during the preseason, the NFL rules on fines are the same for the preseason as for the regular season.
Apparently the league decided that Simon’s hit to Robinson’s facemask wasn’t serious enough to merit any further punishment. Simon got off easy.