You can be a nice guy (a "softie") with no hardened edge and still be a good professional wrestler. This is about attitude (or in The Rock's case, a certain flavor of it). See Daniel Bryan and Kofi Kingston. Both of whom were flatout awful "tough guys" when they briefly went down that route. Because they weren't convincing.
The Rock as a street tough character would be laughable and would come across as satire. It's the same case with your average Hollywood actor who doesn't come form that world and/or doesn't have that wide range in acting ability to make it believable. The Rock can't check either of those boxes off.