Well, there are a few games on that list that don't contain actual blackmail, or focus on it (as Friends in Need does, depending on which route you choose).
For example, I played Point of no return in its early days. And, unless much has changed, the blackmail that was there was not such. I mean, unless memory serves me, the girl you were blackmailing was enjoying it. So that's not blackmail. It is corruption, or a roleplay, depending on the approach. But there is no blackmail if you want to do what they force you to do.
Another example is Descent, which didn't feel like blackmail either.
Special Request or Hometown Trap are indeed games in which blackmail is present at the same level as in Friends in Need (but Hometown Trap has no choices of any kind, no gameplay, so I don't know if it could be considered a game. But the theme of the story is pure blackmail).
Fashion Business does have blackmail plots, but that game lost its way a long time ago, and its history no longer makes sense. In addition, blackmail feels less and less blackmail.
Inside Jennifer, from what I recall, is another game that relies more on corruption than blackmail. Manila Shaw or Wife at all costs, more of the same.
