It seems that the type of “paid mods” bethesda is going for should instead be called “outsourced content”. They’re not exactly “mods”.
“Mods” are inherently unofficial modifications made by and for a third party.
However, this developer-financed content is freelance dev work, essentially hiring contractors to create first-party addons (if Bethesda owns the content, it is first-party content). Mods are third-party content because they are neither paid for nor owned by the owners/developers of the game.
For the same reason, there is no such thing as an “official mod”; that’s just slang for “DLC”.