I'm not entirely certain of the reason you can't play in both leagues, actually. I'm assuming that it is to keep people from winning prizes in both leagues in a season and thus reduce the number of players getting prizes. If you could play in both leagues, I would, for one. But yeah, so far in CL, there are two games posted, and it's the same two players that played against each other both times. CL has been smaller ever since I joined leagues, due to the more difficult requirement of having lots of upgraded cards, but there's something else at play this season; people are choosing not to play CL for some other reason. Personally, I did two seasons in CL first, and then I got tired of the meta, so I switched to BL for a season so that I could use new decks, and I stayed because of the greater number of players.