statistically, so few people use bitcoin, that one might as well round to zero, so governments do not need to care. FB has 2.5B users whom they can easily manipulate, hence governments care.
i.e. a tiny irrelevant niche. I don't think banning bitcoin is a good idea, but a ban would be highly effective because nobody cares enough to risk fines or jail time over something they have no use for anyway.
1. I disagree. There are many effective methods a government could utilize to enforce a ban on transacting on the Bitcoin network. I could think of many technical examples, like the use of weaponized malware and 0-days to spy on the population and uncover users. Yes, some technical people could evade detection, but most people (including most programmers) would be caught up quickly due to opsec mistakes. There is also violence, which would be very effective unfortunately.
2. Even if they couldn't effectively ban transacting on the bitcoin network, the network itself is useless if the state makes it illegal for businesses to accept bitcoin.
3. Strong enforcement isn't necessary since the masses are already uninterested in blockchain tokens except as a vehicle for speculation. If the government made it illegal most people wouldn't think twice about it. Why bother?
Your hypothetical situation is blown out of the water here by existing technology that is clearly very hard to stop. How are governments going with banning torrents?