Marlow was the one that went to MK and then returned to the Thames for restoration by Peter Freebody ( not sure where it is now ). I know John Salter and I think with changing times the larger boats were not needed.
Cliveden and Mapledurham just became beyond economic repair. They operated on theThames for over 50 years without their size being a problem and I have known several of their old skippers who said they were great boats to drive.
Clivden still sits in Salters yard awaiting its fate and was certainly in my opinion the best steamer that ever operated on the Thames.
Many of the Salters built tunnel stern boats like Cliveden and Mapledurham such as Queen Elizabeth, Kingwood and Conort still operate down in London.