The growing DOTA mentality is the biggest reason in my opinion. Many have grown a really REALLY nasty attitude when pvp'ing so if a person makes a mistake for whatever reason he/she will get showered in abusive language.
No one wants to try harder after being verbally abused without even knowing why. And i pity the people that actually have balls enough to ASK what they did wrong... That often takes the abuse to a whole different level. Someone *might* give an explanation but will still flame the "offender" to a crisp while doing it.... I don't know about you but an explanation like that gets ignored by me...
People need to calm down and stop being a**hats over a stupid game.
Explanation you say? Best one I heard was that 'I was stunned'. The stun was SO powerful, it fed into his keyboard and stunned it.
If people want to be better at pvp, there are more than enough guides on these forums or on youtube to help. That's how I learned. People need to take some responsibility because the abuse is down to one thing - the amount of coms you get for a win/lose. It can be almost half, if not less and it wont change until Bioware increase the coms ratio