Closed circuit racing is different to road racing and putting all cycle racing onto closed circuits is not something that should ever be discussed, there’s way too much at stake in terms of development of athletes – you can’t get people up to Olympic/World standard if all they’re ever doing is closed circuits.
Different in terms of how they’re ridden, the terrain, hills etc. Anyone into road racing will know what I’m on about, anyone who thinks that “it’s all just riding a bike” might need another analogy – imagine if all MTBing was at trail centres, there was no access at all to “the great outdoors”. It’d be kind of like that but worse.