AI Doesn't Use Heroes

Colony, Voridus, and Pavium are the 3 leaders that never use heroes in Skirmish matches. They build War Councils, and use other units, but they strangely never train heroes. Every time I let these leaders get controlled by a bot, I do not see one hero unit. I have not seen one Hunter Captain in skirmish that is not mine. Same goes with the brutes. Why does this happen? How do I fix this?
If it helps, I mostly play on Normal difficulty.

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> Colony, Voridus, and Pavium are the 3 leaders that never use heroes in Skirmish matches. They build War Councils, and use other units, but they strangely never train heroes. Every time I let these leaders get controlled by a bot, I do not see one hero unit. I have not seen one Hunter Captain in skirmish that is not mine. Same goes with the brutes. Why does this happen? How do I fix this?
> If it helps, I mostly play on Normal difficulty.

There isn’t any issues I think because you choose the Normal Difficuly and the game lock some options

When playing against AI opponents, I usually play against Heroic (can’t recall if I tried a Legendary opponent yet), and they absolutely use Hero Units. So my guess is it’s a difficulty thing as @Ingegnoso suggested.