Couldn't this be construed as an abuse of a monopoly(antitrust)? They have a monopoly on social networking(there are alternatives, but they are very very small

Couldn't this be construed as an abuse of a monopoly(antitrust)? They have a monopoly on social networking(there are alternatives, but they are very very small in comparison) and they are leveraging that to expand massively in another sphere, namely as email providers.