An update from Blizzard this afternoon confirms the temporary removal of the "guaranteed offering rate" for new Battlegrounds heroes.
If you've been playing Battlegrounds since the introduction of Battlegrounds Perks, you'd know that one of the benefits that you get is that in addition to the 4 heroes you can select from at the start of a game, someone with perks would also be guaranteed to see any new heroes added to the pool in their picks. This system, unfortunately, is not working as intended right now and its randomness isn't really random.
With this being disabled, it is now possible to not have anyone in your lobby see Master Nguyen and Cariel Roame.
Kerfluffle explains what is going on down below. Blizzard expects this system to be fixed in time for the next set of new heroes that are added to Battlegrounds.
In Patch 21.2, we introduced a new system that made it so that new Battlegrounds Heroes would be guaranteed to be offered each game during their early access period (as long as anybody in that lobby had Battlegrounds Perks). The system was supposed to randomly split the offerings between all people in the lobby with early access, but we’re now aware of a bug that is making those offerings not random. We’re disabling the new system and going back to the old early access system for the rest of this early access period (ending September 14). We expect that the new system will be fixed and ready to use again in time for the next new Battlegrounds Hero/Heroes.