Koko lacks a physical STAB that doesnt induce recoil. Blame GF for relying on Wild Charge, while Zekrom is still the only mon that has a decent one. Koko offers a lot of utility and is Pokémon that you usually need from early to late game, which is why taking recoil, on top of Subpar bulk is a bad idea. It seems appealing at first, because you get Brave Bird too, and Elec/Flying sure is decent coverage, but you'll see yourself walled by more threats than the Special set is. And if you can't kill in one hit the Pokémon you're facing (even though max attack Wild Charge in elec terrain is quite busted), you're usually getting KOed back, thanks to the recoil of WC and BB.