Giving the article a read, I came across a few points:
Leave the guy alone
The guy did some pretty nasty things, and is accused of having done even more. It's kind of a place where everyone wants to have a yell at him, and ask him questions. Keeping him out of the public would make his life, well, easier.
He can get into even more trouble
If the guy says something, it can be used as evidence at trial. He may disclose something, or make himself more of a "fool" - undermining his own credibility (if he even has any left), if he were to testify at trial. Worse comes to worse, if something else comes out, he can incriminate himself by proving something, or if he does something else (such as committing assault), he can land up with more charges.
Basically, the media will pressure him, and if that happens, things might not get pretty. Better keep him away from the media. Any confrontations with the media won't result in something positive.
Isn't this damaging both Shkreli's image and their relationship?
Not really. It's just a "standard" thing to do - keep out of trouble, and let the lawyer facilitate any discussions that may arise.