Dont get frustrated because of that. You do well as Lucian and you will improve even more. Having a positive KDA doesn't mean you are gonna win the game, well, this is 5v5 game tho. It happens to all of us. For example, I can guess if game is won or lost at champion select, afeter a 5 years of league I can simply smell that but I just do my best every single time. I main Jungle and it often happens to me that even if I have a full control over map, taking all the Dragons, Rift, Crabs, ganking my lanes often I simply know that we are gonna loose the game. For example, few days ago I had terrible mid and bot, I babysited them so hard, gave them lead, our ADC had 3/0 and our mid was 4/1 ant whenever I am not there, they still struggle somehow. Fuck it I had Vlad mid vs Yasuo, we killed Yas 5 times, guy was 0/5 at 15 min marh and he still had CS lead over Vlad and managed to annihilate him.
Don't listen to people saying "Learn to carry or kys", we all know this is 5v5 game and it's not all up to you. Just do your best. If I have positive KDA and if i secured at least first 2 drakes as a jungler, even if enemy team wins, I feel lije I won that game, simply because I did well.