Because we have to come up with something for pierce armor techs, and shield details are a natural fit. Also, not all techs are "technological advancement," but can also be looked as "Equip" or "Buy." But if we have better names for things, we can change them, so we're open to suggestions and I can eventually make a Pull Request. 

But also pretty anachronical as a tech being researched after 500 BC, I wonder why that even made it in the game 

What's cool about ChatGPT is that it lists sources for its answers:  I know some peoples' cognition has been undermined by overreliance on LLMs, but I'm learning so much:      

I've done that with the hack armor techs in the Forge for the Han just now.  I won't do it for every tech,  but where the differences make sense I will. For instance, the "Wooden Shields" tech icon seems pretty applicable to every civ. 

I like the idea of garrisoning and having a long wait time to get the resources. You can get more than destroying them, but it takes longer