You do realize the max amount of people SWTORs servers can handle are 4500, and the max WoWs can handle are 20,000 right?
Just think about that for one second. SWTOR averaged 350,000k concurrent members on a weekend prime time, WoW has over 1.5 million on a weekday non-prime time.
The dip in subs is because WoW is getting ready to launch another expansion so there is less content to do