Sen was the best in NA for so long early into this game's life. Hence most players gravitated towards them as they were literally NA's best hope, at least that's the way it looked before M3. They dominated Challengers 3 and it wasn't even close.
Sentinels downfall definitely started in M3 though, as even though they were the undoubted best team NA in Challengers 3, they were the 3rd best NA team in Masters 3.
I suspect another weak showing will lead to either Sentinels fans supporting other NA teams or stop watching the pro scene altogether.