So, tell me what I'm doing wrong.

I win lane, I roam, I dominate early game and get massively fed. Our team is massively ahead and we're winning... but then the enemy team starts to focus me, and since I'm the only person that's able to actually do anything, my team then loses the rest of the teamfight, and I just continue losing from there. I split push, and the entire enemy team comes to stop me, and my team just picks their ass and does nothing.

So, what do I do? I have literal potatoes for teammates, and even if I do really well I still lose.