The troops have to be purple for you to get event points. Not every kingdom is saturated with purple troops.
So next time you’re in a battle, count the opponent’s troops that use purple. Then compare that number to the event points you get. They should be the same. If there was one purple troop, you’ll get one event point. For Explore in a random kingdom this is about average! I’m writing a tool to help find the best kingdom to explore for events, and as an example: my numbers aren’t perfect yet but there’s only a 77% chance to get an event point from a random Broken Spire battle. A handful of battles award 2, some battles award 1, and many battles award 0. So if you play 100 Broken Spire battles, you might only end up with 70-80 event points.
That’s a little different in PvP. Some of the meta teams use 2-3 purple troops, and you get to pick between 3 choices each time. So if you’re scouting, it’s easier to get 2 or 3 event points per match.