It isn't really, the fundamentals of life are not much different to where they were a thousand years ago, even if technology has changed and we live a bit longer due to better medicines.
Constitutional monarchy is part of the core identity of the UK, we are simply a country which has zero interest in a divisive President Trump, Macron or Le Pen. Sorry.
Divine Right ended with the English civil war, basic historical knowledge. Parliament now makes the law, the monarchy is just a ceremonial figure.
Constitutional monarchy also has zero to do with religion. Countries like the United States, Brazil, India, Italy, Poland, most of Africa etc are far more religious than the UK but also republics unlike us. Countries like Japan, Canada, New Zealand and the Netherlands and Scandinavia which are more secular like us also have constitutional monarchies like us.
Yes there are also problems in the world but the probability of the entire world being wiped out is near zero too
Charles is already 70. But 50 is relatively young for a monarch and of course it is 50 and late 40 year olds who decide elections and the direction of the country, not 18 and 20 year olds. George of course will also be a popular Prince of Wales and in his 20s when his father is King