Toxic play is caused by:
Broken Mechanics and players exploiting broken mechanics. Some choose to exploit them and "join in the fun" thus causing misery to those on the receiving end.
Inconsistency of team play. Luck of the draw has too big an impact on how your night goes.
Limited time = what did you accomplish with it? - You might have time to log in for 3 games. You might use a few camos you had saved up, you get in there and you end up on a team with a bot, and 40% WR guys across the board playing a unicum division. Your camos are wasted. What little time you have was wasted and you resent the fact that you had what little free time you had trashed. Right or wrong, its how people feel.
Monetization - People like to get their moneys worth. In the scenario above related to time, people may pay for camos or a weekend of premium time. I have had weekends where I win 1-2 games out of 20 no matter how well I played. When people feel they wasted money and got nothing for it, it pisses them off.
Blowouts - Related to the two issues above, this drives people crazy. I don't mind losing if its a good game. I get absolutely livid when I have bots and 40% wr's on my team matched up against unicums and people tell me MM is working.
Player Stupidity - Players doing things like rushing trying to go kill a ship when the game is won and all they need to do is run out the clock. One players stupidity can effect 10+ people.
Annoying Gameplay Features - CV / Subs, absolutely frustrating. When you are the target of either, your game is going to be devoid of fun. They are ships for griefers and are broken in their current forms. You may disagree but I have yet to see any data that supports that players enjoy either and that they are good for the game other than padding WG wallet.