Avoiding Betrayal

[Olaf The Great]

How exactly do you avoid the constant betrayal, I'll bring up two points

1:In RTR I had a Roman campaign, I was conquering Greece with Illryian allies, when both Greeks and Macedonians were no longer a threat, and the ONLY threat the Illryians faced is Macedons ally Thrace, they with a limited infrastructed, and plague ridden army, and several large Romano-Italian armies neaby, attacked a fully garrisoned city, and we quickly pushed them back to a single city, and they became a proctectorate, I destroyed all the buildings in their old settlements and gave it back to them, they had no army and no money.

And as a finisher, the plague had increased and killed their last family member to Ilrryia.(I killed almost all of them during the battles)

2: In EB I had a successful Casse Empire, with all of Britain and Ireland, all of Germania, the Aedui half of Gaul*Arverni a trusted ally*, and A big chunk of eastern Greece(Bribed A Crimerian city).

And Epeiros as another ally, Epeiros had done the same as the Illryians,
first they helped me against the Romans,then betrayed me,the only differense is that they had attacked in massive force,added to this I was still fighting the Romans Germans, and Greeks.
For over 80 years we fought, until both sides had exausted armies.

I'm at a loss here, why did CA implement such A Moronic(Illryian) and Traitorous(Both) AI.