So, I wanted one of my species in a world of mine to primarily use tridents as their weapons. I'm not sure of their location outside of a mesa. I did a little research and tridents were indeed used in ancient combat, but as far as I could tell they were rare and mostly used by fisherman taking up arms. But, I'm not asking for that, I want tridents to be at least somewhat commonplace and not as a weapon to be used in a pinch. Looking on other sites, it seems like tridents are a farfetched thing as a intentional weapon that isn't just to show off since the same metal used to make the trident could make spears instead.
I am not asking for ornamental weapons, nor improvised, and preferably not anything connected to some religion or tradition although that is acceptable. The only benefit I can see for a trident is the disarming factor, but maybe there's something I missed. It's also worth noting this is a medieval-esque technology period, although a little handwavium and suspension of disbelief is acceptable, and worse comes to worst I can always say they live on the coast and choose tridents simply so their weapons have more utility.
In summary, what would cause a military to choose tridents as the main weapon to outfit their soldiers with instead of anything else such as a spear?