You have to have a goal or focus. It is the same thing with MMO guilds. Guilds without those always collapse or break up. I've seen it countless times now. They spam adverts..."Good family friendly and fun guild looking for members!" Then they vanish and you hear later from people that the guild just tore itself apart because they had no focus and people with focus got frustrated and either tried to get it to change or they left entirely. In MMOs either your a PVE, PVP, or RP guild. You unite under one goal with like minded people.
It is no different with gaming clans or communities. One game or idea remains the primary goal no matter what changes. I was in a UT clan a decade ago and this was the case. When we were united under UT99 we were strong, close knit, and ran tournaments all the time. Had multiple teams/etc. Then they decided to branch out to other games. Focus was lost as no one could decide what would be the next main game to play. Clan turned into a skeleton of it's former self as allies swallowed up focused players.
GOIO only has 1 endgame option which is competitive. Sure clans can form up as casuals but you'll only ever play other casuals and no matter how close or good you get, you have no future. Eventually casual guilds break up as people move on. This is similar to raiding guilds in MMOs. When they run out of content, they tend to go dark or members leave for more active guilds. There has to always be something for people to advance towards. All there is in GOIO is competitive. Casuals who refuse or just decide not to participate will stagnate and dissolve unless they find something else to hold their interest. Now when Adventure mode comes, they'll have that. Right now, GOIO is very limited.
I've ran or helped run guilds and clans for over a decade now. I've seen it all before. Groups who come together under a "fun" banner always eventually break up. Especially if they happen to get around any one who plays on a different level than they do because then they start to ask questions like, "Why can't we do that too?" or "Why aren't we doing what they're doing? I want that gear!" On the flipside, super serious groups tend to crumble eventually as well because you cannot keep a noose around people's necks forever. When content runs out, they run out and you have to deal with faster burn out as people generally only put up with a tyrant leader for so long.
Ultimately the best you can do is be a group that walks the fine line between both worlds. Provide for the hardcore player and the casuals. At times you'll lose some because you aren't hardcore or casual enough but ultimately the group survives longer.