Since last week, it seemed as though the writing was on the wall for Omnath, Locus of Creation, and with this week's Banned & Restricted announcement, the card's fate has been sealed. The two most popular decks in the metagame, Four-Color Ramp and Four-Color Adventures, both utilize Omnath, have very high win rates, and made up 23 of the 32 decks used in the recent Grand Finals. As a result, the card has been banned in Standard. The card has been suspended in Historic for similar reasons, in order to promote diversity in the format. Lastly, Omnath was also banned in Brawl, as it was easily the most popular Commander being used, and Wizards of the Coast wants to promote diversity in that format specifically.
Other cards have also been banned in the Standard format this week. Without the dominant presence of Omnath, Adventure decks would be too present and too powerful, so Lucky Clover is being banned in order to make it easier to compete against Adventure decks. Lastly, Escape to the Wilds is also being banned, as an additional step to blunt the power of ramp decks and balance the metagame.
Two other cards are also being banned in the Historic format. Teferi, Time Raveler and Wilderness Reclamation are officially moving from "suspended" to "banned", as WotC has seen increased diversity and interactivity in the Historic format since those cards were suspended. On the other hand, due to the power increase in the Historic format and the falling popularity of Gruul Aggro, WotC has decided to un-suspend Burning-Tree Emissary and return it to play.