Why don't shared files stored in SharePoint lists show up in Tricent?

You can actually store shared files in a SharePoint list, but doing so introduces a set of permission levels that are very different from and much more granular than the ones we're allowed to set via the Graph API (that we use to communicate with your tenant).

So, right now, any shared files that are stored in a SharePoint list won't be part of the cleanup process in Tricent.

If you're interested in a deeper understanding of permission levels in Microsoft, check their documentation right here.