@DrWizardo It's because in this game you disconnect from the lobby server and connect to a match server when you start a game and when it ends you disconnect from the match server and reconnect to the lobby server. Voice chat is not a direct connection between players, has to go through a secure server, for obvious reasons.
You can use Discord or similar for a better experience, but keep in mind that's a different connection and separate app, so it can thin out the bandwidth (network and performance wise) for Apex a little.