It's not illegal to not release your software on a platform. But the mobile market is so top-heavy on both the apps and the games side, that without a few key developers - Meta, ByteDance, Tencent, etc your union is dead in the water - and the top 1% of developers would very much like to more friction for new developers, not less.
>>alexvi+(OP)
If Apple or Google convinced a court you formed a cartel then that's the end of the story. Whether it's a cartel in the eyes in the public would be irrelevant.