The prosecution's forced bribery investigation into Moon Jae-in—they've gone this far

While they were looking the other way to protect Lee Jae-myung,
the prosecution has gone even this far against Moon Jae-in.
Now I see why Lee Jae-myung wanted a prosecution like this so badly.
But I don't recall hearing anything about them harassing his sons during his investigation...
This seems a bit strange. Did they let him off easy?