Magic/random weighted chance, because it’s not a set rotation. Ob Nix & Kiora should have arrived before L2.
The link doesn’t tell you entrances, just exits.
Here’s the current rotation from my database:
SELECT name, available FROM pw_available_history WHERE vault_eligible = 1 ORDER BY 2 ASC
Chandra, Torch of Defiance
Saheeli Rai
Garruk Wildspeaker, 2016-09-08 08:00:00
Sorin, Grim Nemesis, 2016-09-15 08:00:00
Ob Nixilis, Reignited, 2016-09-22 08:00:00
Ajani Vengeant, 2016-09-29 08:00:00
Kiora, Master of the Depths, 2016-10-06 08:00:00
Jace, Unraveler of Secrets, 2016-10-13 08:00:00
Koth of the Hammer, 2016-10-20 08:00:00
Arlinn Kord, 2016-10-27 08:00:00
Sarkhan the Mad, 2016-11-03 08:00:00
Liliana, the Last Hope, 2016-11-10 08:00:00
Sorin, Grim Nemesis, 2016-11-17 08:00:00
Tezzeret, the Seeker, 2016-11-24 08:00:00
Gideon, Ally of Zendikar, 2016-12-01 08:00:00
Koth of the Hammer, 2016-12-15 08:00:00
Nahiri, the Harbinger, 2016-12-15 08:00:00
Garruk Wildspeaker, 2016-12-22 08:00:00
Jace, Unraveler of Secrets, 2016-12-22 08:00:00
Ajani Vengeant, 2016-12-29 08:00:00
Dovin Baan, 2016-12-29 08:00:00
Sarkhan the Mad, 2017-01-05 08:00:00
Arlinn Kord, 2017-01-05 08:00:00
Lili2 is showing up next week which means she’s skipping both Ob & Kiora. There are various other oddities in there - have a look at Sorin, for example.