Allegedly (or apparently), lowering the divider conflicted with the seat design and would have sacrificed seat space - presumably width (albeit minimal). Aside from that, the dividers found on the 77W/77L can be glitchy and a pesky maintenance item. Having said that -- I've also heard the next wave of 787's may have lowering dividers. So really, I've provided nothing concrete here, just chatter through the grapevine. We'll wait and see what the 789's offer.