This is because you have the auto show option when creating channels, You are limited to 10 of these. You can create up to 200 current limit on the channels.
What you can do is create channels with the option, then manage the team and channels and remove the auto show option on the existing 10, and then create more channels. This will still auto show the channels for everyone currently int he Team. Just if anyone new comes onto the Team they will only have the current 10 shown automatically.