AP Supports getting nerfed in mid lane?

When they start to crowd out other mid laners. That said, Morgana and Zyra were both designed for mid lane, then with recent changes, have better luck as support.

Here is what I think.

A champion can have two roles provided one of them isn't too strong. If one of them is too strong and the playstyle is different then the stronger can be balanced without affecting the weaker. If the playstyle is the same then you cannot have both in good position at once - If one is balanced, the other one will either be too weak or too strong.

The game's health is worse when there are champions that are too strong running around. You are therefore left with one option. Nerf the stronger option to a balanced position, unfortunately leaving the weaker option effectively unusable. It sucks but it is necessary.

is not supports lol

When has Zyra ever been nerfed for her performance in midlane (except right after release)? Zyra has been nerfed primarily because of her performance in bottom lane, not mid lane.

Nami has barely ever been nerfed. Her last nerf which shouldn't have happened had nothing to do with midlane where she doesn't go because she was designed from the ground up not to be there.

Because "We don't enforce the meta".