Hot take: people who buy only offensive items aren't dumb, the game is to blame

The item system is not very straightforward.

For instane, I would be willing to bet that a silver player would buy cloth armor vs zed if, instead of it saying +armor it said "zed can't one shot you in the next team fight". And the other option of a long sword said "kill zed 5% faster"

Obviously we can't make them say that, but my point being that, if more people understood how to itemize they would itemize correctly, even at low elo. And the idea that adc players just want to do more damage and never buy defensives is a symptom of a badly explained item system, not the actual desire of the players