I know the real world reason for every troop of the same type (ex. 50 marines) having the same voice is the cost of voice actors and toll it would take on storage, but I wanted to give an in-universe reason here.
This explanation is that there are representatives for each unit on the SoF (and any Banished ships, such as the EC) who relays orders from the tactician (player) to the troops and information from the unit to the representative, who tells the player.
Does that make sense?