that would require remembering them!
for now, here's one of the many no-explanation things I have encountered -- the bottom option is unavailable because we don't have Mass Media researched, but it gives no reason why the middle option is not available(perhaps 2 million gold is not enough?)
Love your Vids and what i do when i go Hunting for Bugs is take a small notepad and write down everything i see i haven't yet done that on C2C as i am still learning this
also i found a weird thing of Disappearing units for AI One turn they got their Tribal Defender unit (200% City Defence unit) the next i notice it is gone and manage to take an entire city with only 1 Cree Tracker

ok he had like 1000 XP


before finally meeting a Second Mexican Deathstack but before that he also destroyed 4 Mexican city's Silly AI is Silly and those Tracker units Early game on a Pangea or large continent map can get almost All the Promotions due to the Animals

but i am now just sharing my experience with those Trackers while distracting from the Bugs
i'll start a notebook or something with all the Building Bugs i find all i state at this point are just things i ran into but try to fix the Anti Animal bonuses as i noticed you get like 500% or so from Both Animal combat and Wild Animal Combat
Just a Recap and simple English version
AI has issues with just Silly unit disbanding (i think disbanding is the right word)
Cree Tracker (and basically any hunting unit on a Pangea type map) can become one men army's able to Rofl stomp most things even when defending against 7 Ambushers

Anti Animal Combat Modifiers on Wild animals can Exceed a whopping 500%

due to the fact Animal and Wild Animal Attack/Defend Bonus Stack and if one is 200 and the other is 300 no way you even get a Scratch on your units
and Money is really hit or miss one game you get just Ridicule amounts the next you are begging for it i guess the only real solution to this is when you find you got just ridicule amounts Start a new game with Different Map Type
Oh and if you want a challenge try settling a city on the other end of the map that Dissolves a lot of Cash