While I do agree this behavior is horrible, I think that new players would have a far better time playing TDM or Duels to improve at the game.
Skirmish is highly competitive. And while playing with high caliber players is the best way to learn, it's also the steepest learning curve you can find. In a game that already has one of the steepest learning curves out there. That's in addition to the fact that in Skrimish every player on the team needs to know their business for the team to win, which puts even more pressure on newbies.
Meanwhile, nobody cares if you suck in a TDM match. You're free to learn at your own pace, and once you get good in TDM and Duels, you'll see Skirmish mode suddenly makes a lot more sense.