It wasn't "disabled" in the sense that it's not intentional
The devs don't just tick the options they want.
The lobby update was a big rework of how custom games worked and so some features can't just work out of the box anymore, it needs additional development time (if it's even possible)
From what I understood now the port is always the same which means that if 2 machines on the same connection have the same port it will cause networking issues but don't quote me on that I could be completely wrong.
The only thing I can tell you for sure is that it wasn't removed intentionally or deactivated or whatever.
LAN simply (sadly) doesn't work anymore on BO2 afaik