It's really sad that main has better setup diversity. Sure they may play Fancy Pants too much, but at least their competitive setups rotate and new things are coming into play every now and again. When I was testing out some new setups with the Role Patrol group, we were overlooked in sandbox but games filled in minutes in Main.
Closed roles didn't always exist. It was suggested back in 2011. When I joined in 2012, sandbox still wasn't completely dominated with closed roles games. Sandbox was just the lobby you could play for fun, instead of the serious attitude in Training or Competitive (for you newbies, training became Main lobby and the dedicated competitive lobby died off). When I started playing and I was my turn to host, I would hand make a setup each time, trying to put a little balance in it as I went. Maybe the Sandbox Setup is so popular out of laziness. It's right there, stickied, and ready to go and you know people will join it at this point so might as well, right?
Did you know there are over 1,200,000 setups saved? Sure most of them will be crap and duplicates, but even out of half of them Sandbox will be playing the same old closed roles one (with the occasional update with new roles, of course).
This is the part of the post when I do a counter point. "But sl0nderman," you are saying to yourself, "the beauty of closed roles is that you get a semi-unique setup each time you host!" Well this is where Sandbox gets part of it's reputation of "not trying." Yes, part of that is the lack of rules, but the other part is that there is less strategy in a closed roles setup than in normal ones. There's little to no way of knowing what roles are in play for the average player in the Sandbox Setup, which in turn causes people to not think about actions as much. Say you went to gun you friend but they were actually a granny and you died. Say everyone just automatically NL'd on the first day but there was an interrogator in play and he just killed the doctor. You can't fault the players for this, there's no way to play around literally every role in the game.
Maybe I've been around too long (which is silly because I've not even close to one of the oldest users on the site), but don't you get bored, Sandbox? Obviously there are those of you who are so done with games that you've complete given up and just sit around in the chat.
I invite everyone who is willing to play games to do a very simple thing. Host a different setup and try something new. There are literally a million to choose from. You'll probably start having more fun that you realize.
EDIT: SHUFFLING THE NUMBER OF PLAYERS AROUND IS FAKE DIVERSITY