I am not sure if the pseudonymous writing of the Federalist papers is a settled matter. But there was a very clear advantage in Hamilton and Madison keeping anonymous, hiding their connection with the Constitutional Convention. The idealized Classic form of debate or dialogue was between two equals , advancing reasoned arguments that would, through discussion, lead to truth. Being associated with the Convention could expose the authors to a circumstantial ad hominem argument: someone could simply claim that they were taking their position because they'd been a part of the Convention and so wanted the Constitution ratified. The ad hominem argument should be a fallacious argument ( that 2 +2=4 is not affected by whether it's written by a mathematician or a toddler) but was and is effective: people tend to distrust arguments made by speakers they dislike or see as biased. By adopting the Latin pseudonym Publius, the writers signaled that they were wanting a real dialogue in the classic sense, where reason, and not bias or factional influence, would lead the speakers and their audience to truth. Or as Madison might say (in Federalist #10) "sacrifice private opinions and partial interests to the public good".

Astroturfing and propaganda and spin have worked because, of course, reasoned debate , and sorting out truth from a blizzard of verbiage, takes time and effort! And of course, it's very hopeful to assume the speakers in a debate will want to find truth. Usually, they just want their side to win. And that was the case, here. The Federalist essays were produced so quickly ( sometimes newspapers published a few a week) that there was little time or space for the Anti-Federalists to mount equally careful, reasoned rebuttal of them.