Yo, why is there no Avenger of Zendikar?
Good question. The main reason is that the point of the deck is to go tall rather than wide. Avenger never did anything really useful unless I could cast it, have 1-2 (or even more) landfall triggers in the same turn, and have
Anger in the graveyard. It just gets wiped otherwise.
I prefer threats that are big on their own (Brontodon et al.) and/or are resilient to removal (
Multani/Xenagos+anything). Omnath, Baloth and
Titania get a pass because they make tokens that are big enough to hit on their own, and which can be useful with all the draw-cards-equal-to-power cards.