Zwift, Trainerroad, etc. are good for people looking to train to become better cyclists. You do largely need to bring your own setup, which can often be complicated (although you can then get a setup that mirrors your outdoor work).
I am referring to fitness training, not training to become a better road cyclist, and I suspect most people that use a Peloton or go to Soul Cycle have no intention of training to become better at road cycling. They are doing so to become fitter, and Peloton's training is specifically aimed at improving various areas of fitness. So when I refer to training, I am referring to training to improve specific fitness goals and not training to become a better cyclist.
I have no interest in becoming a good cyclist, but I am looking to improve my fitness across a variety of metrics. I also weight train and do other stuff, but I have found the Peloton approach to indoor cycling well suited to helping meet specific fitness goals.