The thing that bothers me the most (as a toplaner) is to see that everyone snowballs out of control, and at that point what are you going to do against a 14/1 midlaner? Or a 8/2 ADC? Even if you are ahead the game isn't winnable
/rant
Sometimes the other team simply has more experienced players and better ganks. There could be a smurf involved. Don't worry though, this doesn't happen to just you. :)