My girlfriend goes to the gym but also paid for a yearly subscription of videos to workout at home. It saves time, more convenient, flexible time wise (not always) and you don't have to worry about getting to the gym or looking good. Being at the gym can be a motivator for sure but how many people wanted to workout but just couldn't get themselves there? Lots of people.
Programs like Zwift have been very successful. If you haven't heard of it, it's an online virtual world for people who want to bike or run with other people. I think Zwift is a model for future fitness and workouts. Versions of it are already done with rowing as well so why not other things?
I had a girlfriend who was a fitness instructor and I can definitely see the advantages of having gym's hooked up with videos or live streaming of workouts from places all over the world. Some of their workouts are like rock concerts and definitely get those watching the video pumped up. I think it's much more than a fad.