These players do this to "punish" people who arent playing to that persons desired level.
Its kind of like:
a player who gets gold/diamond in ranked
Makes a new account
Gets to 30 and starts ranked
Starts in bronze (for whatever reason)
THEN
Immediately expects EVERY BRONZE PLAYER to play like a gold/diamond. Why? well they is Gold/diamond on another account so they expects everyone else to play to THEIR Level. They expect bronze players to play like gold because THEY are gold. And if the player doesnt stack up to Thier expectations then they flame, insult, degrade thier team and say "Well you are playing like trash so I am gonna troll"
Again its all about thier own ego. Expecting everyone else to be like them.
I mean how many of these players brag about how they are "Gold/platinum on another account" and when they get saddled with bronze, who need to maybe learn. Instead they get brow beated, degraded, insulted, and torn down by these "gold" players. Everyone is so full of themselves that they dont think they need help, and No one actually tries to offer it anyways.
With most of these "elite" players, instead of suggesting "Hey that item doesnt work that well with that champ (insert optional reason why), "X" item might work better for you" is replaced with "LMAO OMG Ur build, So Fking pathetic. ur so bad. so trash ahahahaha. Uninstall league and go kill urself lolz"
Of course there are some players who refuse to acknowledge any help and respond with "OMG STFU dont tell me how to play" But its kind of a gamble. Some may just take a chance and try it to get better results. But again, because the advice is not even offered in the first place, no one even tries. So people go on thinking they are the best, they get a swelled head, and end up expecting everyone to thier level, and trashing (and trolling) anyone who doesnt meet thier expectations.
But as with most cases. This is just my own 'aspie" logic (yeah I do have aspergers, for those planning to reply with the "r u retarded' response)