The reason I get ever so slightly grumpy over this is that seemingly a bunch of people feel it is right and proper for Larian to dedicate resources to make the product better for their platform specifically while purposefully ignoring all other platforms. I don't know why that is reasonable?
It is no less a messed up perspective than if I was to argue that Larian should make DLSS mandatory for anything beyond lego resolution, and to hell with scrubs who chose to buy an AMD card. They knew what they were buying. Never mind that it isn't too sensible, but it surely isn't a nice attitude, is it? Definitely rubs me the wrong way, I have to say.
I can see a strong case for using Steam Workshop if a game is only really sold on Steam at launch, or if the dev is small and doesn't have resources for more. But in this case, some users are literally asking for Larian to dedicate resources to fragment the modding community and encourage mods to be exclusively available to Steam users, and there's no real reason for it.
The reason I'm only slightly grumpy is because Larian is pretty big, the community for BG3 is likely to be reasonably big, and so neither the resource investment nor the fragmentation really ought to be too severe. But I'd still dramatically prefer if Larian focused on a more platform agnostic solution to modding rather than tying it to Steam workshop.