I think that makes sense, but it still seems a bit arbitrary, I don’t see bookshops having these issues
In contrast, part of the SE editorial philosophy is that it tries to host the best (based on academic scholarship, translation quality, academic acclaim, etc.) version of each text available in the public domain, which excludes that "something for everyone" sort of play available to a commercial bookstore. You could rightly argue that this is losing something (it's good to have multiple translations to compare if you're reading a text for critical purposes), but the SE editorial philosophy avoids a certain amount of confusion and clutter for the general reader. So there's a deliberate (you could call it "arbitrary" in some sense, if you wish) tradeoff being made here.
So modern versions of e.g. the Bible could not be in Standard Ebooks. So easiest to not carry any translations.
Bookshops have no problem with this as part of the purchase price will go to the copyright owners of the translation.
It's true, modern versions of War and Peace can't be hosted at SE, but those modern versions generally don't reflect revolutionary leaps in archeology :)
There are modern translations that are permissively licensed and are of surprisingly high quality. See the NET Bible as a prime example. It's also the only one I know of with good translation notes that can be had for free.