Sadly, play style comes into it. I have one city I started in 2016 which is only just entering orcs. I've come to a hard stop in all of the recent events because I can't complete any more encounters in the wild without diamonds. I have 6 Phoenix artifacts, 4 stonehenge, 4 mermaid, and 2 gingerbread and have not bothered to place any of the buildings.We all know that events always ask to scout or complete provinces; it's player strategy ensure that this won't negative affect its own game.
I have done every single event since 2017, and I never had this problem. I'm not a genius, I simply do only necessary scouts.
Players do not all progress at the same speed.