Some of the oldest professions have a notion of "privilege" with sensitive information. Client-attorney privilege, Physician–patient privilege. While some of these have been eroded at various times, there was a reason for their creation.

These services probably need those levels of privileges as well. Even a warrant shouldn't necessarily compel the yielding of information. Instead a request can go through the organization which immediately responds in the negative, but then behind the scenes asks a client if they want to voluntarily testify against some unknown relative of theirs (I think put in these terms, a lot of people will say no).

The rationale being the same: if the police have easy access to this information, people won't trust the services enough to make optimal use.