That's not true. Vanilla had 1-8M (best increase in subs than any expansion had), BC had 8-10M and Wrath had 10-12M . In some statistics, BC had 8.5-10.5M/11 and wrath 10.5/11-12 (or 12.5M), but whatever, your numbers seems to be really biased.Also, it was a VERY flat peak in WotLK.. TBC had 11,5M subs, up from 6M (vanilla).. WotLK had 12M subs, up from 11,5M (TBC).. So, which is better? Almost 100% increase or ~5% increase? It would be more precise to say, the decline started in WotLK..
For me, BC was the expansion that started the wrong path (flying mounts, focus on raids, no more RPG elements, difficult modes, etc...) and of course, Wrath helped with alot of other things (more difficult modes, streamlined raids, etc...), but this is just me opinion, because I prefer other type of meta-game than this days. But I'm not saying that BC or Wrath were really bad expansions, both had the elements to make new subscribers.
I'd love if they just showed gameplay, as in a real dungeon or quest with some seriously solid additions. It won't happen, will it fuck, but that's the only thing I'd be truly interested in seeing
Nothing with maybe a smug lolumad when somebody asks about flying after the day
Wrath baby and proud of it