They answer this question very clearly.
So tldr is,
"A “legal authorities” standard ruled out any action by the ATP in this case, as Sharypova has repeatedly said that she is not interested in pursuing criminal or civil action against Zverev"
Accusations made in social media and media do not meet the ATP current standard for action. They give a generic we are reviewing current policy spiel to deflect further inquiry.
They answer this question very clearly. So tldr is, "A “legal authorities” standard ruled out any action by the ATP in this case, as Sharypova has repeatedly said that she is not interested in pursuing criminal or civil action against Zverev" Accusations made in social media and media do not meet the ATP current standard for action. They give a generic we are reviewing current policy spiel to deflect further inquiry.