Perhaps also having production costs covered by a publicly funded broadcast organisation. At that time the BBC were moving away from informative and educational programming (watch early Dr Who or the earlier work of Michael Palin etc) into more pure entertainment. I suspect a lot of the quirky comedy projects would have been a hard sell commercially. 

carlosfandango

bitcoin

Orange Pill Diaries: The Lebowski Brothers

siggy47

I guess this is the billion sat question that's been asked for years. I guess there's no a straightforward formula.

Just enjoying yourself and not having overbearing production constraints might be a large part of it.