I think the idea is tied similarly to peoples love of factions, as seen during our trips to Ravnica, Tarkir, and Alara
You can't remove oil counters from it if it's not on the battlefield, so you won't lose the game if it had only one oil counter on it before leaving the battlefield
Overall, Mono Green has access to a variety of great rares at varying mana costs
I often find that if I have the mana untapped, people have to assume that I will use it to keep my Fortress alive, and they swing on elsewhere
It slows down opponents in the typical fashion before casting Upheaval and Psychatog in the same turn, then swings with a huge creature on the following turn
AssassinatorAcer didn't specify if this deck is better at going first or second at the start of the duel