As I understand your point it has absolutely nothing to do with it being illegal to not have a SIM card. Your point is simply that it is impractical not to have a SIM card because that makes it difficult to do bank transactions. Big difference, and using 'illegal' in this context is highly misleading.
I think the implication is that if you wanted to function without a SIM card, your only way to do that would involve eschewing all above-board fiscal infrastructure and working with the grey/black market instead.
It's like being an outlaw, or a member of an untouchable caste: sure, you could just hide in a hole forever and wouldn't be breaking any laws, but in order to do anything you'd have to do it in a way that breaks a law.
