It's something that was added exclusively to Fallout 4. On Skyrim SE pages you can still use the "Mirrors" section to link to Bethesda.net
Well it was exclusive until SSE came out in September 2016 I think it was, but I agree with Arthmoor it doesn't make sense to have that for one game and not both as both games have mods hosted on Bethesda.net.
Besides, still having like that only confuses people and I am quite sure that Bethesda will some day in the future release other games that has mods hosted on Bethesda.net. So, why not use mirror for both games.
Maybe they will release Fallout 5 in let say 3-5 years from now and we all are waiting for TES 6 in the next 1-3 years.
That's kind of the reason why I don't like the implementation of this at all.
It's a hack specific to a handful of games. In this case, yes, it's the two most popular games on the site. I'd say that mirrors/permission make that whole section unnecessary but it was added in response to the initial wave of mod piracy when Bethesda.net opened. As far as I know (and from speaking to one of Bethesda's CMs) the problem isn't anywhere near the scale it was before. If there are still pirated mods over there, they do need to be reported to Bethesda through the Bethesda.net site - I know that as long as they have valid reports they will remove your content.
If this becomes a trend I'd be in favour of a site-wide update to permissions rather than tacking something else on. A combination of the "upload to other sites" and "convert to other games" permission do generally cover posting on Bethesda.net, but I appreciate this isn't abundantly clear when referring to consoles.