I had often wondered about the complete change in preference, one day over coffee with a male friend (T), the subject came up. He also liked these shows and told me they gave him a break from the outside world. That's when I got it, these 'reality' shows allow the viewer to step away from their own reality, to take a break from any issues or complications and get lost in someone else's drama, problems and celebrations. I have found that sometimes the drama on these shows is so extreme and escalates so quickly, that on reflection my own life, for a moment does not seem so chaotic.
They also allow the viewer to have a much needed relax, the storylines are not usually so complex that they need full focused attention, I often watch them when I have had a busy day at work or have had an upsetting day and need to unwind and not really think about anything for awhile.