I guess the reason was "sloppy firaxis coders" ....
This is some of it
https://forums.civfanatics.com/threads/new-version-1-2-1-november-23-2021.674256/
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[Bugfixes]
- FINALLY fixed AI making Defensive Pacts above the limit, this was happening because Firaxis's deal code for AI to AI deals functioned as follows:
AI #1 asks for something and decides how much gold/stuff it's worth, without asking the other AI
AI #2 accepts automatically, even if their value would normally be "IMPOSSIBLE!" or dramatically different
This terrible "wild west" system has been fixed at last
Thanks to Milae for fixing AI to AI deals
Thanks to Aristos for finally providing the save that I was able to debug

- Fixed remaining cases of nonsensical bribed wars and other trades of impossible items (a side effect of this bug)
- Fixed AI making Defensive Pacts with civs they don't want to (another side effect)
- Fixed AI being unfairly more friendly to each other compared to the human (another side effect)
- Fixed AI rarely having resources available for trade (another side effect)
- Overall, diplomacy/trade should now be more dynamic and fair to human players!
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