As others have said, talking to people is good. Ask them what it is about the game that might not be thrilling them so much. Ask them what could be done differently that might perk them up. Ask them if there are important things in life that are taking priority - can you change the day you play to make things easier for them? And so on...
One thing that might help, paradoxically, it to play less often. I don't know the situations of the people in your group, but six to eight hours a week is a lot for many modern adults to commit to. Folks have other things to do in life, and may be running into conflicts. When your game runs frequently, it may be hard for them to keep it high in priority - there's always next week, so missing one session's not a big deal.
So, you might try running every other week. Give folks space for other things, and through scarcity, make each session count that much more.
One thing that might help, paradoxically, it to play less often. I don't know the situations of the people in your group, but six to eight hours a week is a lot for many modern adults to commit to. Folks have other things to do in life, and may be running into conflicts. When your game runs frequently, it may be hard for them to keep it high in priority - there's always next week, so missing one session's not a big deal.
So, you might try running every other week. Give folks space for other things, and through scarcity, make each session count that much more.