As of right now, there are four WWE Superstars who will not be flying to Saudi Arabia for
Super ShowDown on June 7th and those are Daniel Bryan, Aleister Black, Kevin Owens, and Sami Zayn.
In the case of Bryan, he decided to no longer attend events in the country after going for the first time last year and his opinion on the matter has not changed. However, Dave Meltzer has now revealed that Owens was asked by his family not to go, while the fact the Saudis hate Syrians may have also played a role (which is why Zayn isn't going).
As for Black, it turns out that it wasn't actually his decision; WWE decided he shouldn't attend because his tattoos are of a religious nature and the company presumably doesn't want to offend the Saudis (who they have a big money deal with).
Right now, it doesn't sound like any other Superstars will be pulling out but we'll keep you updated.