Of course they would make reasonable attempts to contact them, but as you've said it appears anecdotally that none have reported or engaged with the police and if all that's given is a name or social media profile it's unlikely the police can know easily who these people might be. A couple of hours work to bottom that out tops if noone engages.
So then we are back to the same place. What investigation can they do? What crime are they investigating? If those screenshots or messages have been presented by a victim or witness who created or received them and is a victim there's something to work with. If not you have nothing to investigate.
That information though would be held as intelligence certainly, and in that sense investigation into the a suspect lasts forever. If someone makes complaints against the same person in the future that intelligence could potentially be used in some way.
It appears to me you are reading things into the nature and circumstances of the (lack of?) investigation that are not there to be read. Exactly why I said from my very first post on the matter that Twitter is not the place to make these reports, the police station is.