The thing is pick-up games. People say they suck. The thing is, THEY ARE NEVER GOING TO BE AS GOOD as squad games. A lot of it is, people getting better at the game, then getting annoyed when people aren't as good as them, then leaving.
Just lower your expectations of pick-up games, learn to enjoy the game with your fellow human-being and stop taking it all so seriously, then it becomes fun again

Over the years I've seen a fair few players join and then leave on this path, a bit sad really, but if people can't get this message into their thick skulls, then so be it.
As for those who leave because of the attitude of others - well your leaving is just going to make it worse isn't it! Stay and be a force for good!