Sex appeal. Peloton is built on sex appeal. The instructors lead workouts wearing makeup, jewelry and bikini tops (well, the female ones anyway). Vox has an article [1] looking at SoulCycle and it sounds similar: instructors were good looking and exhorted to be incredibly thin. That said, it's a great way to get a good 30 minute cardio workout in.
The Peloton instructors are also universally the best spin instructors I've ever encountered, and I've been to countless spin class in every large US city over the past decade. Some have come close, but being able to have world class spin instructors in my living room has been the huge selling/sticking point for me.
It's pretty difficult to define, and the definition will vary person to person. It's similar to asking what makes a good coach? For me it's a combination of energy, attitude, verbal clarity, and also a personality that I find attractive and pleasant, i.e. the type of personality that I'd enjoy spending an hour listening to and taking instruction from. Also of course a sound knowledge of form, technique, and healthy strategy.
I'd say simplicity, too. I'm a long-time cyclist and a 4 year Peloton owner. I work in tech (obviously) but I frankly have only the vaguest idea of what combination of computers and displays and sensors and adapters I'd need to use to Zwift. And the slack channels I swim in seem to be full of folks always fiddling with what kinds of sensors to use and how to get them to reliably communicate.
You can just swipe a credit card (or, probably, ApplePay 1 button purchase) and have it show up at your house and work.
[1] https://www.vox.com/the-goods/22195549/soulcycle-decline-reo...