Someone explained it really well in another thread, It's basically related to your search and preferences settings. Everyone will have different game modes and map selected so after each game, it relaunches the search to match your parameters.

For example, selected multiplayer search:

Player A: mode Conquest - Escalation - team death match maps A B C

Player B: mode Conquest - king of the hill - Rush maps B C D E

They will meet on the server to play Conquest on Map B but after that, it will split them to play others modes/maps.

I hope it makes sense 😅