I agree, it’s functionally true he probably wouldn’t have been able to join anyway but that’s not necessarily what this kind of thing is about.
Their announcement was more than just banning Brock Turner. They told us (and everyone who would want to join) they don’t tolerate this and if one of their members had done this, the member would have been subject to severe penalties. They’ve set a precedent and they’ve talked about it publicly.
Them announcing this also sets an example for other sports organizations. They should all be looking at themselves right now and saying “Wait, does our policy cover this? We need to have a policy to cover this. We need to make sure we’re ready in case one of our members does something like this.”