The game needs a feature to kick players who are not actively playing. It’s a huge waste of time for other players to play a map with 0 chance of victory because of several players doing nothing.
I’d suggest that if a player hasn’t built or moved a unit in 12 hours, send an e-mail warning. After 24 hours, kick them.
Give an incentive for new players to join active games with open seats, such as bonus hero coins at game end and/or valour points when joining. The valour points can be traded as the player needs for gold or mana to make up for their forces being behind from former-player neglect.