Because it is not your country. This incident just uncovered the lie that you have been told your entire life. If you need permission from someone else to bring your wife and your kid into your house, then it is not your house, it is "their" house. And you are not a citizen, you are a serf.
If you were really a free man and that was really your country, once you legally demonstrate to the state that you are lawfully married to your wife, and the kid is yours, that should be the end of the story.
Somebody somewhere will be making some
Fabian argument justifying why you can't bring in your wife and kids without the state's approval. But the truth is that once the government becomes the provider of its citizens, he also becomes the owner of its citizens. He can then dictate if you can or cannot bring your wife and children to live with you. The road to serfdom could not have been any more explicit. There is always a trade off between liberty and security.