There are 193 UN member states. Then add to that the Vatican, Taiwan, and dozens of overseas (or otherwise special) territories having ISO 3166 country codes. Can you trust all those governments to reliably play their part in such a system?
This is part of why the current setup works - it isn’t dependent on the cooperation of any government agency to function.
That said, I would never respect the DNS TTL of such a scheme, for my own use cases. I'd query each of them once an hour, latch the last response forever, and delay propagation of a new response for a full week that it stayed stable before serving the new record.
The timezone database was not created for the benefit of governments, it was created for the benefit of users and vendors.
People who have to live their lives under corrupt/incompetent governments have enough problems on their plate already, without the added indignity of making it harder for them to get their computers to show the correct local time.
It might be possible to use that for the information of now - to answer the question of "what is local time for me based on UTC?" or "what is local time for someone else now?" ... but what about the information of yesterday? When it was 12:01 PM in Chicago in 1948, what time was it in Hong Kong?