Last I've checked, workshop never hosted any nvde mods, or things of an advlt, or AO nature.
Try and sneak something like that by in AU and watch as the game gets banned from store shelves, and still possibly sued for a breach in some sort of agreement, or for trying to dodge an accurate rating.
ESRB, PEGI, CERO, ACB etc, All exist to classify games based on their content, and determined age suitability.
ESRB being: Ec, E, T, M, AO
PEGI being: 3+, 7+, 12+, 16+, 18+,
Australian Classification Board being: G, PG, M, R 18+, and X 18+ which is essentially AO.
Guess what nobody wants... An AO rating.
Sometimes they'll have a fine print like "Online interactions not rated by..." That's more in terms of your online play.
In the case of PC, whether its permitted or not, mods will happen and cannot fully be regulated, and therefor, not exactly able to be "rated"
In the case of consoles, they can. First off, mod features needs to be an integrated feature for the game/console. There needs to be a way of obtaining, and accessing mods through the console/game, and in all honestly it'd probably be much more streamlined than PC modding, meaning easier for people who might not be old enough to play in the first place, to get their hands on some less than age appropriate mods. Pair that with whatever terms and conditions Microsoft, and (potentially) Sony may have, and the scrutiny the game/companies may come under for an integrated, and streamlined modding experience on the console by the ratings boards for allowing their game to be altered to that of a state that doesn't match with their rating, should make more than enough sense as to why they wont allow that extent of modding on the consoles.
You want simple "add new thing here", "alter companion look" mods, the console will still be good for that.
You want limitless (and unscrutinized) modding, PC has and always will be the way to go. It's the one with no rules. Whatever rules it has are hastily bent, and or broken.