Because Netflix pays them either way, I would imagine. Breaking a contract on a sure thing to the tune of tens (hundreds?) of millions of dollars for a maybe is a large business risk.
Reputational damage is going to be far more Netflix than the NFL if they totally club it.
That and this fight is going to likely be an order of magnitude more viewers than the Christmas NFL games if the media estimates on viewership were remotely accurate. You’re talking Super Bowl type numbers vs a regular season NFL game. The problems start happening at the margin of capacity most of the time.