Nobody has even been indicted under the Logan Act for 166 years, and nobody has EVER been convicted under it, during its 219-year history, despite pretty much constant examples of American citizens dealing with foreign powers in a way that arguably undermines administration efforts. The reason is that enforcing the Logan Act in a way that punished such behavior would clearly run afoul of the First Amendment, so there's no point in even trying to indict people. As much as presidents would like to be dictators, when it comes to deciding what our foreign policy efforts are, that runs counter to our principles. We're all citizens with a right to speak our minds to whoever we want. To punish that, a narrower theory of law is needed -- for example, making a case that a given meeting amounts to a conspiracy to commit campaign finance fraud, or that classified information was wrongly shared.
Trump, of all people, should be glad that's the case, since half his cast of reprobates met with representatives of the Russian (or Israeli) government, during the campaign, in ways that could be seen as undermining Obama's foreign policy efforts. If the Logan Act were enforced the way conservatives wish it was enforced, against liberals, that would set a precedent for locking up just about every major player on Team Trump, including his son, son-in-law, AG, etc., as well as plenty of other high-ranking Republicans