It’s an accounting issue. It is also why all coupons, gift cards, etc. expire. When you buy a domain, or get a coupon, the company basically has to treat that as a debt that the company owes you, and this has to go on the books as a kind of liability. No company want too much of that.
The DNS isn't 50 years old. There's absolutely no certainty your payment for the last year's will mean anything. Also if you're older than 35, you'll probably be dead. If you're not dead you probably won't care about the domain any more. Certainly all current politicians and the current political and economic systems will be dead. It's unclear there will be any reason to still have the domain and that it won't be blocking some innovative economic activity. It's unclear there will still be an internet.
It won't protect you against the country hosting the registry being nuked but it will likely shield you from future price hikes because not honoring pas renewals would quickly get the registry a reputation for being a fraud. Which is probably also why there is a limit - no registry wants to be bound by arbitrary long timed liabilities.