The main legal benefit is §230 of the Communications Decency Act, which has never required platforms to refrain from exercising editorial control in order to receive immunity (in fact, one motivation for this law was to encourage platforms to engage in exercising editorial control without incurring liability for doing this).
(I can see political pressure now and in the future to say that some platforms should have some kind of neutrality and/or transparency obligation in order to get this immunity -- but under current U.S. law, they don't.)
