[Joe]

The saying goes "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do".  So the answer is almost certainly yes.  They just may not be aware of it.

Beliefs change, but choosing not to take part in something for principled reasons very often means you will not come to regret it. 

(I don’t know the reasons why some declined, but assume anti-monarch sentiment is a factor for some.)