It's a bit of a surprise, I wouldn't have expected them to change the trademark Infinity Engine formula. It was pretty bold of Bioware to take the D&D rules and squash them into a sort of 'simulation' of sorts.
I can’t of course speak for Larian, but from the interviews I gathered that they believe that real-time combat in BGs was a necessity due to popularity of Diablo rather then bold creative choice. They might even be right, one would need to ask Bioware folks about it. Larian doesn’t do real-time, because they don’t believe it is a good fit for the system. And they are not wrong, even If audience found things in it to love.
In addition, their Divinities sold really well and serving their existing audience is financially smarter then old Baldur’s Gate fans,who might/might not like this game no matter what approach Larian takes, also Larian is very coopfocused, and making game turn-based just makes things easier and that’s design Larian already worked with.