Shields are reason ...
Since their AC bonus is counted if you have equipped one, rather than holding it in your hand.
Larian support told me in a recent email that the AC bonus from a currently unused shield was intended to be removed for the full release, so I think we can dismiss this particular feature as a consideration for the future. Thankfully!
Good to hear. I think that's a good thing, too. I would have been very surprised if they didn't get it right. After all, increasing stats works by holding weapons, doesn't it?
https://baldursgate3.wiki.fextralife.com/Splinters+of+a+Giant's+Might
Then it should be easy to implement for shields as well.
