To further emphasize on one of their brand features, further promoting it. It started with the DOS games, when no other game of the genre (maybe Wasteland? I'm not sure) involves verticality as a combat factor. "Hey this is something we came up with that is super cool and you should really use it. It's ok if you don't want to use it but you'll probably get wrecked by enemies who use it, so yeah you'd better use it".
I'm not saying that Larian can't do that, but as a player I find these mechanics pretty bad and pointless, just that. In my opinion, the reasons I mentioned in the thread are good enough for you to stay in high ground, but beyond that, there's the advantage/disadvantage issue, that completely spoils the balance in my opinion.