Why aren’t Zetas monetized?

It will come...just wait for it. G12 was also exclusive to promote investments in characters that would get you G12 stuff (mainly TB teams). Now that many have farmed those teams, they put them into the store for crystals. Will also happen to Zetas at some point in one way or another.

I think they will introduce more ways to indirectly obtain zetas, so that you have to invest in certain characters...