But it's not the only system. Factorio, like Rimworld, has a huge mod scene and has it built into the game instead. Which has the advantage of working outside of Steam on a DRM-free (or not-steam) copy, which like another reply says, just makes Steam Workshop another form of lock-in on Steam.

Except the forced updates can easily break mods and managing your mods with the steam workshop is garbage. Even the terminology is bad, subscribed doesn't mean download and install to me.

Workshop isn't perfect but it's a good enough solution for most games. Especially simulator games where the authors knew how to make a sim but have no idea how to handle mods (for example)

I think you can stick to a specific version if you want with rimworld, many mods are updated fairly fast although and even if they haven't been updated tend to work anyway.