[dragonwriter]

> They're only now dealing with something that happened over four years ago?

“The wheels of justice turn slowly, but grind exceedingly fine”.

> Am I missing something?

Yes, the history of the crime and related events related in the complaint linked fromm the press release. Compressing a bit:

The various Twitter accounts used in 2016 were under false names, a Congressional Candidate for whom Mackey worked outed Mackey as connected to the “Ricky Vaughn” the accounts in late 2018, the FBI interviewed that candidate and a documentary filmmaker who has interviewed “Ricky Vaughn” in 2018 and confirmed the identity in late 2020. There's lots of stuff not directly germane to the charges against Mackey about the narrative left out, but there was presumably more investigation to attempt to identify others involved because several co-conspirators are listed only by Twitter IDs.