I will be honest its always been there but its alot more prevalent than it was.
Back in the day it was alot more about isolated elitism, people would be elitist within certain circles of community and that toxic attitude was not healthy for the game. The biggest issue is that its like a seed thats been planted, and grown for over 11 years.
That seed has finally bloomed and the problem is, it was always there to begin with. Its mostly because blizzard created a strong stigma to helping others by simply designing raiding, pvp, and most of their content towards "competition" rather than "cooperation". So instead of working together, you find alot of people would rather have all the glory to themselves and not share it at all.
This was the folley mistake, and the reason so much shit happens.
Hearthstone is an example of a game you can never be mad at, it has no chat box, no need to communicate, because only one person and one other person can play with each other at any time and you cannot chat to your opponent in any way to taunt or piss them off.
Its one of the only well designed examples of competition ive ever seen done right, because it focuses entirley on trying to compete, rather than trying to brag about competing.