My bike is on a trainer, and I see the following down-sides:
a) My bike on a trainer is really loud. Can't do it early; can't do it when the baby is sleeping, etc.
b) It's a moderate pain in the ass to hook and unhook. Not a huge pain in the ass, but I certainly didn't do it any time of the year it was feasible for me to bike to work.
c) It's dirty. I mean, the bike. I dislike washing the tires so I can bring it indoors even a couple of times a year, never mind if it's coming in and out constantly. And never mind the fact that even washed, my wife sure as hell isn't letting me bring that into a corner of the bedroom.
d) My bike has exposed chains and gearing that, if I'm not mistaken, the Peloton and similar bikes do not. I've got a toddler.
e) Indoor exercise bikes are usually reasonably set up to let you have somewhere to put your phone, or ipad, or kindle, etc. Bikes on a trainer do not. When I'm working out indoors, that makes a big difference for me.
This hasn't been enough to convince me to buy a Peloton, but I can certainly see why someone with more disposable income (or square footage) would.