Why advice doesn't work in LOL!

No first hand experience. Generally "advice" is given my people who were only in that situation for 3 to 9 games. So, they cannot give advice on something they barely did. And anyone can avoid bad players for some time.

Basic advice. Nothing tailored to the actual person strengths and weaknesses. Just saying get better but not even knowing what happening in the game. When is the player dying? How often? What is he/she doing wrong? None of this is answered. It's almost like these people are reading off a script.

No first hand expeience! If you don't experience it do not give advice. And I mean, play a game with the person. Actually try to figure out how to make them better. This is a game, you have play with them to make them better. Words don't work. Watching streams doesn't work. Only first hand/up close help works with most people. Otherwise don't bother helping.