Because the screw-up was caused by Blizzard themselves… or, rather, their inaction to correct the issue.
When Season 24 ended on Asia… it ended incorrectly. Not only could players log on in “seasonal mode” (remember, the season was supposed to be finished), but they could also log into non-season mode. That allowed players to play “Season 24” after the season, collect some ethereals, and bring them into non-season (and use them in GRifts). Blizzard was informed of this issue a few hours after the “end” of Season 24 on Asia.
I made a couple posts (the first one here, some 7 hours after the “end” of the season). At that time, I could not grasp the entire issue… so I made other posts later… in this topic in Bug Report.
Long story… Blizzard did nothing, Season 25 started with leftovers from Season 24 including ethereals… and suddenly they woke up. Knee-Jerk reaction : reset the season.
I suppose it was the only thing left to be done… should had been done on 5 Dec, but…
Bite the bullet and good luck in your games !
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P.S. : something else I should have mentioned…
Obviously, I am not the only player who reported these issues… just look around. There are reports in Technical Support, General Discussion and Bug Report. There are other reports that we made… not in public view, but directly to Blizzard. Our MVP MissCheetah raised the issue with them the first time during the Dec 5th week-end… and then again later. No reaction from Blizzard.