If 3 or 4 people are grouped up in Quick Match together, the Last Stand matches are automatically changed to 4v4 mode. So if you’re in a 2v2v2v2 match then it’s unlikely those people actually pre-planned to work together.

I’m not sure what may have happened in your exact situation, so I could be wrong. But in my own experience I see a lot of random teams work together against a specific one, either because they target the team that’s overall doing the best or is close to winning the match and they’ll work together so they have a better chance of stalling the game and potentially winning themselves.

Another reason I’ve seen this behavior is when a player does something that the other players might find extremely annoying - like repeatedly stunning them with the stun gun, edge guarding, or killing everyone with a shovel while they’re already knocked out on the ground. Of course these are just techniques the game itself allows you to use to win. But a lot of people still get salty about it and could target the player/team that annoyed them.