I think it's just mainly human nature to stick to what you have been doing or use what has been advertised to you. Many people refuse to use generic drugs and want to pay more for the name brand drug even when the generic is manufactured in the same plant by the same company and they just throw a different label on the bottle and charge you 50% more for it. I will often pick a generic over the counter drug and just look at the ingredients and compare to the name brand and if they match 100% then I use it.

With bleach people generally think of bleach as being dangerous and toxic and why would you want to put that into your pool ? Won't it fade your swimsuit ? The fumes could kill you !!!! etc. Mention that it's exactly the same stuff as liquid chlorine sold at the pool store but even less strong and their eyes glaze over in confusion.