Bethesda has recently updated their procedures for uploading Fallout 4 mods to their website by adding the extra step of requiring your account to be linked to Steam. This is intended to prevent the unauthorized uploading of PC modders’ work for use on consoles.
The change came with the most recent update to Fallout 4 last week in preparation for the porting of mods over to PlayStation 4 consoles. When mod support first came to consoles at the end of May, some modders found that their work had been taken from non-official sites and uploaded to Bethesda’s website for use on consoles. Bethesda has created a channel where these modders can file DMCA complaints to have their work removed, but hopefully this new change will help prevent such occurrences in the first place.