Why do they do it ?

Try to resurrect a dead concept that is.
This is a completely implausible take on Hyacinth Bucket's early life. As far as the acting was concerned, although the actress had all of the characters mannerisms and accent off, she wasn't the greatest of actresses - and it would have taken the greatest of actresses to pull off the dire script.
If you are going to make dialogue repetitive - make it good dialogue - not this unfunny forced "comedy".
The whole production had the air of a stage farce.
"Daddy" was overacted to caricature lengths - I expected better from the actor - but again - it was probably the direction that was at fault. The sisters were more restrained and more bearable to watch.
Note to script writer - I don't think that "upwardly mobile" was a phrase used in the fifties.
I hope this is a one-off.