There exists already anti-trust laws to deal with monopolies. Why does there need to be another new law that, instead of punishing the monopolistic companies,

There exists already anti-trust laws to deal with monopolies. Why does there need to be another new law that, instead of punishing the monopolistic companies, gives them the right to maintain their monopolies as long as they promise not to discriminate on filtering their traffic? Why can't the government pursue these literal monopolies using the DOJ with existing laws?