Dynasty had so many reasons it eroded.
The Moldivia Massacre might have given them the biggest numbers ever but how do you top that where cliffhangers are concerned?
The Rita/Krystal story was horrible.
Catherine Oxenberg was fired and her recast was horrendous.
The Colbys spin off did them no favors.
Dallas:
Patrick Duffy leaving the show left a big hole to fill. They tried filling it with Dack Rambo.
Bobby's return was handled poorly.
Viewers returned the following season to see Bobby's return. They left the other soaps in the dust!
But the it was all a dream backfired and Dallas never recovered after that.