^ This.
It's market strategy. They want to keep the toxic players just as happy as the non-toxic players, because $$$.
The only time they actually punish people is when those people might cause Blizzard to earn less $$$ (bots, gametime sellers, ...), not when they are annoying other players (last I know even item duplicators don't easily get banned either) because the official Blue response then is:
Originally Posted by Blizzard Entertainment
The ignore function can be used if someone harasses you.