Hopefully they are trying to test adding one more and see if the “performance issues” are still there, so we may actually get another tab in S18.
or
They decided to stick with 13 tabs after the last PTR, then forgot to change it actually in the game as they have done with other stuff.
or
This is a smokescreen to distract all the Barbs from there severe neglect the last several years.
or
They are just trolling you guys on the PTR, so you get your hopes up, then they can smash your dreams just before the patch goes live.