Which is sensible; the problem is favouring some players so much they capture an entire industry. Free market is a perfect ideal, it can't exist in the real world.
Obscurity increases the bar, and now, some actors will be prevented just by it, some delayed and some not affected at all, but after all you dont know who is attacking you and their skills!
It's just a good component of a defense in depth approach. Where it's bad is when it's the only defense. Putting a sensitive server behind port knocking will cut down on 99.99999% of random internet IPs spraying attacks at it, so it's worth doing. Just don't rely on it for the only auth check.
How would the country’s internal intelligence services know what’s happening? Yes, by spying. That’s literally their job and they have assets in every critical area in a country. Every institution, every major industry player, they are monitored to a degree by the internal intelligence in every country in the world. There are more nefarious reasons to do this but the ostensible one is that if it’s of strategic importance the country needs to know everything there is to know.
The companies also do a lot of spying themselves, every bit of info could give them an edge.
What if you receive notification about transaction that you didnt make? :)