It is SchemeS league because we will test other schemes too, Alt-F4 is only the first one. SIBASA planned all this, so if he is organizing, I will trust the way he planned the league.
If we allowed many schemes at the same time would be way more complicated to organize. Imagine if we had Wormopoly Party, Board Game, Get Frank and many complicated schemes to stablish rules at the same time, it would be a lot of work and would be a mess, I guess. But I agree that with more schemes maybe more people would have interest on playing the schemes, and more schemes would be known.
This will be our first attempt, Alt-F4 is handy because it doesn't require big PNG maps to upload on a forum, the author and the fans of the scheme are active right now and we already have a Cup of this scheme that facilitates to people understand the scheme and how organize things.