From my experience within 70+ years of having known the Organization, encouraging specific secular work was never done by the Society. Especially in the 1970s in Britain, window cleaning was a helpful well paying business which was flexible enough to fit around the Society's demanding schedule. You see, as we were a smaller religion in England at the time, we all had mutual connections all over the country and we told them either by letter or telephone or when we visited them about this fantastic and easy business which could help "put God's Kingdom first", some may even have had relatives who emigrated to the US or Australia and shared the same message with them. As you can imagine, some independently minded elders at assemblies and conventions subtly promoted it at the time when the Society definitely was not encouraging jws to pursue a specific lifestyle, only to find work that paid all the bills and helped them to live and which never conflicted with bible principles. Of course, I am presumptuous to assume if the British JWs started the craze, but it seems that for a pre-internet era word soon spread around across to many brothers and gradually many took up window cleaning as well as other cleaning activities (some chose office cleaning).
I did it for a time in the 80s, and I hated it. Some clients were so obnoxious and demanding. Such is the way of the British in some areas with our "stiff upper lip". I went back into accounting as I had done for many years previously and I felt for all those brothers who remained window cleaners until retirement, it was an especially dangerous job in those days, due to the fact this water fed pole system wasn't yet introduced and became a more preferable option some time in the 2010s in the area I lived.
Yes, the picture is sad. Let's not remember however some of these men made the sacrifice because they genuinely believed they were doing it to increase their ministry activities.
I am stunned at the number of Jehovah’s Witness men now who work "full time" as window cleaners, especially now they don't have to report time and if they do as regular pioneers it is a measly 50 hours! It's a doddle now. Call me a grumpy old man, but some of those witnesses who work "full time" as window cleaners earn 10 times more than my state pension, those bastards!