@Riot Conqueror Design Question

I'm sure its been asked before, but why is conqueror basically the only rune that gives AD and isnt adaptive?

Precision is already a tree fairly heavily skewed towards ADs, why make the keystone so? Its not a huge deal, but there are a couple champions that I think it could be great on but im hesitant to try it on. Namely Singed and Rumble, but maybe Morde. There are few champs who would get the AP bonus, but why exclude them entirely? Which one was so scary that it was axed entirely? True Damage Equalizers sounds pretty nasty, same with Morde Ult.

Idk I was thinking of unconventional conqueror users and these ones came to mind in my search