Why do Riven and Zed get so much consistent free AD?

Seriously, Riven level 1) 20% on auto attacks level 6) 30% on auto attacks + 20% total AD with ult level 18) 50% on auto attacks + 20% total AD with ult

Zed's is based on the rank of his W +(5/10/15/20/25)% Bonus AD

the closest runner up is Yi with 10% on his E

then you also have champions like fiora, tryn, noc, or olaf who get flat AD with skill ranks, but those flat amounts still tend to have less value than the % increases.

Obviously i leave out the big mustached elephant in the room , but only because he has very low scaling across his abilities, while both riven and zed are AD casters. I mean even Yi could fit into this same category, but w/e.