As Wizards itself even stated in their ban post: "Field of the Dead ramp decks represented 42% of the field at Mythic Championship V and maintain both a high play rate and win rate on MTG Arena and Magic Online." Everyone was expecting the card to be banned after an official ban announcement was moved up to today: that happened, and it's the most significant ban in Arena history since February's Nexus of Fate (in best-of-one games).
The changes will be effective on October 24 in the digital version of Magic: Arena, so expect everyone to get in some last-minute wins before that actually happens (and your wildcards back when Field is removed from the game). It will be banned in Magic Online (the older school client) today and in the tabletop version on October 25. Arcum's Astrolabe was banned in pauper, but that does not impact Arena. The next ban and restricted announcement will happen on November 18, 2019. About that.
A lot of players were expecting Oko, Thief of Crowns to get hit, which was always going to be a very rare occurrence given that Wizards isn't likely to ban a powerful marquee Planeswalker fresh off the release of a new set. But even I was fully hoping that some form of Oko tech, like the one mana-cost (forest) ramp creatures, would help avoid a situation where opponents are squaring off against a turn-two Oko. No such luck.
Although Oko was vaguely mentioned as "acceleration into planeswalkers," for now, Wizards is going to "continue to monitor the health of the environment." While Field decks are gone, Oko decks (along with ones themed around adventures and card draw) will shoot up in popularity, and they'll be a thing for a bit.
This is standard after all: if one archetype loses its luster, another rises in its place.
Banned and Restricted Announcement [Wizards of the Coast]