Why is there no loss protection for players who rage quit or force losses?

tl:dr: Had a great team that became the victim of one player despite their composure. I think there needs to be a level of protection against this because morally upstanding players do not deserve to be dragged down and this kind of toxic behavior will only spread to other players and contribute to keeping the community toxic.

While I understand such protection would need to be carefully implemented to prevent players from bullying out others to force it, I'm wondering why there is still zero protection for your LP from players on your team who up and decide that you are going to lose a game. There are simply games where 4 players will be victims of one player's actions, and regardless of how they compose themselves there is no protection for that.

In this particular game our Lucian left before 15 minutes outright stating that he was quitting. I wasn't entirely invested in the chat at that point and had not said anything to him, but he had been very vocal towards his Leona. I had not seen any flame or trolling directed towards him at all, just him flaming his support as his lane wasn't going his way. I will say though that I had seen everything typed out, but I am confident that he was not flamed this game.

The game was 12-12 before even 15 minutes, I had Nasus 40 CS behind me and both Neeko and Rammus where performing well. While Draven would be problematic lategame we would have had a strong advantage midgame. We where all (aside from Lucian) also communicating with each other and working towards goals as a team.

I mentioning that to make it clear that this was a very winnable game, and that the rest of our team was working together nicely and not flaming each other. Even after Lucian left I didn't notice any toxicity including after failed FFs while the team still worked together. Lucian even returned after ten minutes, presumably to see if we where close to loosing yet before leaving again. We went as far as to ask him politely to stay because it was winnable and did not flame him at all. This was not a clusterfuck of a game heavily snowballed to one side where one player faces the ire of the rest of his team for having a bad game and has to leave to preserve his own sanity. This was one player who was given a team that was ready to work together and be patient, where he decided to attempt to flame and humiliate his support in chat before leaving in a tantrum, deciding by himself that four other people must now lose because he couldn't handle what happened in the laning phase.

So I'm left to wonder why there is no protection from players such as this. Again I am fully aware of the logistical difficulty of implementing such a system fairly, but I need to state the facts. My team where not just better players, but the more mature individuals. They do not deserve a full LP lose because of the childish actions of one person. I can say this definitively because this was my first game in Gold and I technically lost 0 LP anyway, but my team lost the full amount. I do not see how there could not be some measure of protection for players in absolute circumstances like this. My team are victims, I don't see it any other way. It's heartbreaking to know that their reward for staying calm and collected in these circumstances is to lose full LP. Heck, had one of them lost their composure and let slip certain particular words, they might be closer to the banhammer than the Lucian is. I do not consider this to be fair, and I strongly believe that this lack of security is a key motivator for players becoming like our Lucian. I would be very interested to hear the opinions of Rioters on this one, as I am still open to the idea that what we have now is simply a necessary compromise players must endure. I'm not currently convinced of that though, as I genuinely believe these players deserved better.