Why does Tahm get adaptive AD while Taric gets AP?

This makes absolutely no sense with their kits. Tahm has a spammable poke spell that scales with AP and his E scales really well with AP while Taric's AP scalings are pretty bad, especially early game before he has 4 points into Q. Taric's passive is the biggest reason why I want adaptive AD on him. It straight up doubles his attack speed.

What are items you want on Taric? What are items you want on Tahm?

It sure makes sense that you give Taric AP and Tahm AD.