#1 Austin is in no position to take a bump
This is probably the saddest reason on this list, but there is always the chance that Stone Cold Steve Austin's body wouldn't be able to handle something as physical as being attacked by The Fiend. Remember that Austin's neck was broken at SummerSlam 1997, and though the Texas Rattlesnake was able to return to the ring afterward, it has been many years since Austin was an active wrestler.
Retiring in 2003 after his WrestleMania 19 loss to The Rock, Austin has avoided even hinting at a return to the ring. Though he recently took a stunner from Becky Lynch on his 'Straight Up Steve Austin' show, it's possible that the former World Champion's body wasn't ready for a full-on attack.
If this is the case though, the question remains why WWE would even have Wyatt hint at confronting the Rattlesnake at all, as many fans speculated that the two would meet each other based on Wyatt's tweet. Whatever the truth may be, don't expect the Eater of Worlds to confront the Bionic Redneck anytime soon.