If there is still a level 1 on a team when a game ends, that team shouldn't lose LP.
I have no earthly idea why a system to compensate for people never connecting has not been implemented yet.
I can understand the hesitance to reduce LP losses for teams with AFKs. That's a system that could be abused, and if a team fell behind it could quickly devolve into flaming people to leave so the rest of the team doesn't lose anything. Penta queues could abuse it. These are all relevant reasons to be careful when approaching this topic.
But NONE of these drawbacks apply to people never connecting. You can't plan to have someone that DCs instantly, and it's almost always an instant loss. The ONLY possible drawback I can think of is teams using it to win-trade in higher elo, but this seems like something that would be very easy to detect and punish accordingly.