Psychological Mafia

I don't see any major differences, except that the newspapers might be shorter.

There are many differences. It's hard to list them all from memory. But, for example, the fact that in psychological Mafia, you can reveal yourself as any role, lying or telling the truth from the very beginning, fundamentally changes the gameplay.

I still don't understand why it can't be considered a specific case.

Because the specific case is Mafia with clues, not the other way around. If you compare it to the original parlor game, psychological forum Mafia is not much different from the original version.