Again, If you're going to make a group in general and you want everyone to be active and such, Just be dedicated and willing. Plan it out thoroughly and make adjusts if needed. As everyone basically mentioned, don't make it just another chore and just have fun with it.
Sometimes these groups that demands such a thing, forgets that this is a game, a game that is a part of people's lives and such and it's just a second escape for most. They don't need to be weighed down with even more responsibilities and all that, we get enough of that from Real Life itself.
I can understand if it was about.... one time you hear from them and they don't show up ever again ( unless something unexpected happen , because it will happen ) and then ja, you can do like a group clean / wipe, what have you, but don't just do it just cause.
Again, everyone has their ways of doing things, you don't necessarily HAVE to join the group if it's not your cup of tea. Sometimes groups are willing and open to suggestions on how they can improve, even increase activity and you're free to voice your opinions as long as you don't take it overboard if not, just kindly tell them and leave. Who cares what they may do, it's YOUR choice in the matter. Being active all the time ( and even I'm starting to see this now, hoping to adjust ) for multiple times a week for a certain amount of time, is stressful and I try to avoid such a thing if they're not willing to work with me or even others in the group.
All & All, not everyone can simply be pleased, whether it be in-game or not. In real life, if you're working, you gotta try and adjust if it's dire and if you truly need it, but in-game, you really don't need to be a part of the group because you're still giving up part of your time to work with theirs and it's not you're getting paid to do so or anything.
But ja, might not be making sense but still, if you don't want to be a part of a group for this or you see it as not fair, just leave. Simple as that.