The 89% chance is (I THINK) based on teams not sitting their players, which...I mean...
I think that 89% drops to 50% if the Bills and Steelers rest their players. Here we are rooting for the Steelers and hoping they don't have any major injuries tonight. Talking about sacrilegious. I got them beating the Colts next weekend. After that things could get pretty shaky because I don't have the Dolphins losing to the Raiders.
I assume that ESPN is putting a percentage on how likely it is for each team to win each game. Then applying the various combinations of wins/losses that each team needs to make the playoffs.
But from just a statistical standpoint, there are 6 more games the Ravens need one of which to be a loss. (0.70) ^ 6 = .118. So if each team is 70% likely to win their games, then there is a 11.2% chance they win all 6 and the Ravens stay home. On the inverse, there is a 88.8% chance one of those games is lost.
If you wanna say the Bills and Steelers rest in week 17 and those games are 100% wins (which is likely not true), then it's 4 contests. (0.70) ^ 4 = 0.24 or 24% likely that all the games are wins and the Ravens stay home.
The 3-0 week this week for the direct competition definitely makes things much less improbable moving forward.