There 3 games (at least) visible in the Board Browser (in Create Game tab) that are unplayable. They are:
Whittl'em Down
Diplomacy
Base 9.
Why is that?
What do you mean by unplayable? Are you unable to start a game? I was able to bring up the Whittle 'em Down game starting menu just fine (though I didn't actually try to start a game).
The 3 games do not show up on the main board browser or on the pull-down "select" menu under "Create Game." They do show in the board browser under "Create Game." If you select, however, one of those 3 games in that board browser, they do not seem to become playable on the "Create Game" page.
Good spot that is actually a bug - those are all Beta boards so unless you have enabled the view of Beta boards (on your settings page) they shouldn't be visible in any of the pages / lists.
However they are appearing on the board browser and if you have Beta turned off you can still see them there, when you select the board it doesn't correctly appear in the Create Game page.
I've fixed the bug now.